01First run
What to expect in the first few days, and why patience matters more than anything else you do.
Open the app and tap Scan. Almost immediately you will see a long list of devices — phones, televisions, routers, headphones, smart plugs, cars. This is normal and none of it is meaningful yet.
SentryRF does not decide anything from a single sighting. What it looks for is repetition across places and times: a device that is near you at home, then again at the shops, then again at a friend's house is behaving like something attached to you. A device that sits in one place forever is furniture. That distinction takes days of ordinary movement to establish, which is why the first day is mostly noise.
Give it two or three normal days before drawing any conclusion. Do not change your routine to test it — the app learns your routine, so an unusual day teaches it the wrong thing.
This manual describes the Android app. An early Windows version is also available and covers core scanning, but it does not yet match the Android app feature for feature — most of what follows applies to the phone.
02Permissions and why each is needed
SentryRF asks for a small set of permissions. Each one maps to a specific detection ability, and the app degrades gracefully without any of them.
| Permission | What stops working without it |
|---|---|
| Nearby devices (Bluetooth) | Everything. Bluetooth scanning is the core of tracker detection — AirTags, Tiles, SmartTags and similar are all found this way. |
| Location | Two things. Android legally requires location permission for any Bluetooth or WiFi scanning, even if an app never looks at your coordinates. Beyond that, SentryRF uses your position to tell the difference between a device that stays in one place and one that follows you — which is the entire basis of follower detection. |
| Background location | Detection while the app is closed. Without it, scanning only continues while SentryRF is open on screen, and a tracker following you during the day goes unseen. |
| Notifications | All alerts. This is the one people miss. |
| Camera | IR Lab and the camera-lens finder in Physical Sweep. Not used for anything else, and never for recording. |
| NFC | NFC Lab only, and only while that screen is open. Android grants it without asking, and it is never used in the background. |
| Microphone | Ultrasonic and acoustic detection inside Physical Sweep only. Audio is analysed live and never recorded or stored. |
Notifications matter more than they look. On Android 13 and newer, if you decline the notification prompt the app will keep scanning perfectly but will never tell you anything — and Android also hides the scanning icon, so it looks like nothing is running. If you see a red banner on the home screen saying alerts are disabled, tap it and grant the permission. A detector that cannot alert you is decoration.
03Keeping it running in the background
The most common reason people think SentryRF "stopped working" is Android's battery saver quietly killing it.
Many phones — particularly Samsung, Xiaomi, Oppo, Realme, Transsion (Tecno, Infinix) and other manufacturer skins — aggressively suspend background apps regardless of what the app asks for. Fix it once:
- Android Settings → Apps → SentryRF → Battery
- Choose Unrestricted (sometimes called "No restrictions" or "Allow background activity")
- On Samsung, also check Settings → Battery → Background usage limits and make sure SentryRF is not in "Sleeping" or "Deep sleeping" apps
- On Xiaomi/Redmi, set Autostart to on and battery saver to "No restrictions"
This does not make the app drain more than it needs — it only stops the system from cutting scans short.
Choosing your scan interval
In Settings → Scanning there is a scan interval slider, from 30 seconds to 5 minutes, defaulting to 60 seconds. This is entirely your choice and the app never overrides it.
- 30–45 seconds — fastest detection, noticeably more battery. On an older or smaller-battery phone this can drain faster than a slow charger keeps up.
- 60 seconds (default) — detects a new device within about a minute. Sensible for most people.
- 3–5 minutes — battery saving. Detection still works; it just takes longer to notice something new.
04Teaching the app what is normal
Ten minutes spent here is the single biggest improvement you can make to accuracy.
Open Devices and work through the list. Anything you recognise — your phone, watch, earbuds, television, printer, car, games console — open it and tap It is Safe. Each one you mark does two things: it silences that device permanently, and it teaches the app what your normal environment looks like.
You do not need to identify everything. Mark what you know; leave the rest. Unknown is not the same as dangerous, and the app is designed to work with a partly-labelled list.
Living in a flat or busy building
Radio passes through walls. In an apartment block you will see dozens of your neighbours' devices, and this is not a sign that anyone is watching you. Two things make the list usable: mark everything you recognise as Safe, and judge by behaviour rather than presence. A neighbour's television in the same spot forever is not following you. A device that appears at home, then at the shops, then at a friend's house is the one that matters — and that is exactly the pattern SentryRF is built to find.
05Threat levels, and what each actually means
Levels are automated assessments of behaviour over time — not verdicts about people.
| Level | What produced it | What to do |
|---|---|---|
| LOW | Something about the device's shape or reputation crossed a low threshold. Usually an unfamiliar device with no history yet. | Nothing. Noted for context. |
| MEDIUM | Either a stronger reputation signal, or mildly suspicious behaviour that has persisted. | Worth a glance. Check whether you recognise it. |
| HIGH | Behavioural evidence — the device has been seen with you across different places or times, or repeatedly at unusual hours. | Look properly. This is the pattern that matters. |
| CRITICAL | An active tracker confirmed as following — for example an AirTag separated from its owner that keeps appearing with you. | Investigate. Use Sound Locator to find it physically. |
Consumer devices like phones, laptops and watches are deliberately capped at Medium unless there is real behavioural evidence. A phone that shares a signal characteristic with something suspicious is interesting, not actionable — so the app refuses to escalate it on that basis alone.
06Safe, Watch and It is a Threat
Three actions on a device, three different meanings.
It is Safe
Permanently trusts the device. It stops appearing in Suspicious, stops generating alerts, and the app treats it as part of your normal environment. Use it freely on things you own or recognise — this is how you train the app.
Watch
"Keep an eye on this." The device stays in the list and continues to be scored, but you have flagged it for your own attention. Watching does not lower or raise its threat level.
It is a Threat
The strongest signal you can give. It marks the device as a confirmed threat and applies that to every address the device uses, not just the one you tapped. It also teaches the app's learning system what a real threat looks like for you.
You can escalate from Watch to Threat at any time. Both actions stay available together — marking something as watched never removes your ability to call it a threat.
Changing your mind
All three can be undone from the device's screen. A device you marked as a threat shows a Not a threat button: it removes the threat mark without trusting the device, so it simply goes back to being scored like everything else. A trusted device shows Untrust, which returns it to normal scoring.
What Safe never does
Some devices can never be silently trusted in bulk, no matter how ordinary they look: known trackers (AirTag, Tile, SmartTag and similar) and surveillance hardware (cameras, hidden cameras, smart glasses, drones). A "trust everything here" shortcut will always skip those categories, because the cost of quietly trusting a planted camera is far higher than the cost of one extra tap. You can still trust such a device individually, from its own screen, if that is genuinely your intent.
Devices the app trusts on its own
Every device is analysed on every scan, and that never stops. The on-device AI watches how each one behaves over time — whether it moves with you, whether it turns up in different places, whether it appears at odd hours — and scores it. Anything that scores as a concern stays on your list regardless of this setting.
What the setting changes is the quiet ones. A device that has sat in the same spot for days, scored clean every time, and looks like the router or television it claims to be stops being repeated back to you. It is filtering what you have already been told, not skipping the check. This exists because an unusable list is its own kind of failure: a screen of two hundred devices tells you nothing.
You control it. Settings → Detection → "Trust familiar devices automatically". It is on by default and you are asked about it during setup, so you know it is happening. Turn it off and nothing is trusted automatically at all — every device stays on your list, including your own router and television.
Because many of those devices will also raise alerts, turning it off asks you to confirm first, with Show every device? Choose Show me every device if you would rather judge everything yourself, or Keep AI filtering. You can change it again at any time.
Trackers and surveillance hardware are never trusted automatically. Not by this setting, not by any shortcut, and no matter how long they sit still. A tracker that stays in one place for three days is precisely what a planted tracker looks like — so the app refuses to quieten it. That refusal is deliberate and is not something the setting can override.
Anything trusted automatically says so on the device's own screen, along with the reason it was trusted and an Un-trust button beside it. And a device you un-trust stays un-trusted — no automatic process will quietly trust it again later.
If you want to start from nothing, Settings → Data Management → Remove All Trusted Devices clears every trusted device, including the ones you marked by hand. Expect a noisier list afterwards until you mark your own things again.
08Understanding why a device was flagged
Every device screen explains itself in plain English.
Open any device and the What we found section explains, in ordinary language, what the app observed and why it reached its conclusion. It covers how often the device has been seen, whether it moved with you, whether it appears at unusual hours, and whether a tracker is reporting itself as separated from its owner.
Further down you will find the supporting detail: signal strength history, the times and places it was seen, its manufacturer where known, and the technical identifiers it broadcasts. You do not need to understand these to use the app, but they are there when you want to check the app's reasoning rather than take it on trust.
Sometimes two facts sit in tension — for example, a tracker reporting itself as separated from its owner while also appearing to live at your address. The app will say so plainly and give you both explanations rather than picking one. A device that belongs in your home and is separated from its owner is either a household member's item, or something that was placed there.
09Scan
The live view of what is being detected right now.
The Scan screen shows devices as they are found, with signal strength and classification updating in real time. Scanning runs in cycles: a burst of Bluetooth and WiFi listening, then analysis, then a pause until the next cycle at your chosen interval.
There are two visual styles for this screen — a standard radar and a tactical phosphor display — switchable in Settings → Display. They show the same data.
The radar does not show direction
This trips people up, so it is worth stating plainly. Where a device sits on the radar is not its real bearing. A phone has one antenna and cannot tell which direction a signal arrives from, so the app cannot know where a device physically is. Devices are placed around the scope for readability, with distance from the centre reflecting signal strength. The sweep you see rotating is the display animating, not the devices moving.
If you want to find where something actually is, use the Sound Locator and follow the beep. The reasons are explained there.
Clusters of WiFi devices that never move
In any built-up area you will detect a great many WiFi access points, mesh nodes and televisions, because radio passes through walls. A group of them sitting in one place, even with high scores, is almost always neighbouring infrastructure. It is worth ignoring unless one of them starts appearing in different places you go. A device that stays put is not following you — and being followed across places is the pattern the app is really looking for.
Scan profiles
Beyond the default, the app offers profiles tuned for particular situations — a quicker sweep, a deeper and more thorough scan, and a parking-lot mode for checking a vehicle. The default profile is what you want for everyday background running.
10Devices and device details
The full inventory of everything ever seen.
This list is long by design — it is the raw record, not the app's opinion. Day to day you should be reading Suspicious, not this. Use Devices when you want to mark things Safe, look something up, or check history.
The threat breakdown
A device's screen can show exactly how it was scored. For ordinary devices — a neighbour's television that is always there, a smart meter — the breakdown starts folded away under Tap to see how this device was scored, because a page of scores reads like an accusation when nothing is wrong. For anything you have marked as a threat, or that the app rates Medium or higher, it always opens in full.
MAC address rotation
Modern trackers and phones deliberately change their Bluetooth address regularly to resist tracking. This is good for privacy and awkward for detection: the same physical object appears as a stream of "new" devices. SentryRF groups these back together using stable characteristics that survive the rotation, so one tracker shows as one device rather than fifty. Occasionally you may see a device merge or split as the app gains confidence — that is the grouping correcting itself.
11Suspicious
The screen that is actually talking to you.
Suspicious shows only devices that crossed a threshold, ordered by severity. If you check one screen a day, make it this one. An empty Suspicious list is the app telling you it found nothing worth your attention — which is the normal, expected result on most days.
12Sound Locator
How you physically find a device you have decided to investigate.
Open a device and choose Sound Locator. The app beeps faster as the signal gets stronger, exactly like a metal detector. Walk slowly, sweep the area methodically, and follow the sound.
Getting good results
- Move slowly. Radio signal strength fluctuates constantly; walking fast produces noise rather than direction.
- Sweep, do not stand still. The signal only becomes directional when you change position.
- Expect it to be approximate. Radio reflects off walls, metal and water — including the human body. It will get you to the right area, then you search by hand.
- Check the classic places: bags and linings, under seats, wheel arches, boot trim, behind sun visors, inside cushions.
Why the arrow drifts, and what to trust instead
This is the most common question we get, and the answer is physics rather than a fault.
A single phone cannot measure which direction a radio signal comes from. It has one antenna, and one antenna gives you strength, not bearing. The arrow is not a compass pointing at the device. It is an estimate the app builds by comparing signal strength at different GPS positions as you move. That has three consequences:
- Standing still, it has nothing to work with. It will drift or spin. That is the honest output of no new information.
- Indoors or in a vehicle, GPS is weak or stale, so the estimate is built from old positions and points at nothing useful. You should see an orange GPS stale warning. While that is showing, ignore the arrow completely.
- Distance is derived from signal strength, which changes constantly as your body, walls and the phone's orientation block the signal. That is why the number jumps.
What actually works on one phone: the beep
The beep rate is pure signal strength with no GPS involved, and it is reliable. Use it like a metal detector, not a map.
- Walk slowly in one direction for five to ten steps, and listen.
- Faster beeping means warmer. Slower means colder.
- If it slows, turn ninety degrees and try again.
- Hold the phone away from your body and keep it in the same orientation. Your hand and body block the signal, and this causes much of the jumping people notice.
That method will bring you close. The arrow will not.
For real direction, use two devices
Accurate bearing needs more than one receiver. See Paired Sweep below, or SentryPod, which uses a much better antenna. This is a physical limitation of one handset, not something software can solve.
Paired Sweep: two or three phones together
Two or three phones running SentryRF can work as one instrument. They connect directly to each other — no internet is needed — and share signal readings, so the app can work out where a device actually is instead of guessing from one point.
Setup takes about thirty seconds.
- First phone: open Sound Locator, tap Paired Sweep, then Start as Master.
- Second phone: open Sound Locator, tap Paired Sweep, then Join Sweep.
- Third phone (optional): the same as the second.
- Wait for Connected. The master then picks the target device, and all phones begin tracking it.
What you get depends on how many phones you use:
| Phones | Result |
|---|---|
| One | Distance only — the same as the normal Sound Locator. |
| Two | Distance plus which side of the room the device is on. |
| Three | An estimated position on a map, typically accurate to 2–5 metres. |
Where you put the phones matters more than anything else.
- Spread them at least 3 metres apart. Further apart is better.
- With three phones, form a triangle. Do not put them in a line — a line cannot resolve position.
- Use different heights where you can: a table, the floor, a shelf.
- Keep them still during the sweep. Movement ruins the result.
- Every phone needs location permission enabled.
A confidence bar shows whether the readings agree. Green means they do. Red means the environment is noisy — usually people moving between the phones and the target, which scatters the signal. Ask everyone to stand still and try again.
If a phone shows Searching, check that Bluetooth and WiFi are on — both are used for the direct connection, not for internet. If one phone shows No signal, the target is out of its range; move that phone closer.
Using a Wear OS watch as a second point
If you have a paired Wear OS watch, it can act as a second receiver without needing a second phone. The watch runs its own Bluetooth scan and sends its signal readings to your phone, which combines them with its own. Because your wrist and your pocket are in genuinely different places, this gives the app two measurement points instead of one.
The watch also shows the live signal reading on its face, so you can search with your phone still in your bag or held out at arm's length — which removes some of the interference your body causes.
Tell the app which wrist you wear the watch on: Settings → Alerts → Watch on right wrist, shown once a watch is connected. Paired Sweep uses it to place the watch correctly beside your phone, which keeps the direction estimate honest.
The screen also shows a compass and, when there is enough quality position data, a directional estimate. If your GPS is poor — indoors, underground, in a car park — the app deliberately falls back to signal strength alone rather than showing you a direction it cannot justify. A confident arrow built on bad data is worse than no arrow.
Making a tracker beep does not prove you own it. Most trackers will play a sound for anyone who asks. A beep confirms the device is there and reachable — it says nothing about who put it there.
13Physical Sweep
Using the phone's own sensors to examine one specific place.
Where scanning listens for radio broadcasts, Physical Sweep looks for things that do not broadcast — hidden electronics and camera lenses in a room or vehicle. Use it for a rental, a hotel room, a changing area, or your car.
| Sensor | What it looks for |
|---|---|
| Magnetic (EMF) | Powered electronics and motors — and also metal and magnets in devices that are switched off. Strong readings near an unexplained spot warrant a closer look. |
| Camera lens finder | Uses the camera to spot the retro-reflective glint of a lens pointed back at you. |
| Infrared | Night-vision cameras illuminate with infrared invisible to the eye but visible to a phone camera. |
| Acoustic / ultrasonic | High-frequency emissions from some electronics, above human hearing. |
| Light & pressure | Environmental context that helps interpret the other readings. |
How to sweep properly
- Move at a few centimetres per second. This is the mistake everyone makes — sweeping fast gives the sensors nothing to work with.
- Hold the phone close to surfaces, and cover them systematically rather than randomly.
- Pay attention to anything with a view of a bed, a shower, or a changing area — smoke detectors, clocks, chargers, air purifiers, sockets.
- Expect false positives from real electronics: wiring in walls, appliances, speakers and the phone's own hardware all produce readings.
There are two layouts for this screen — a standard view and a tactical view — with the same detection behind both.
Finding something that is switched off
The magnetic sensor does not only find working electronics. It finds metal and magnets too. A camera that is switched off still has a magnet in it. So does a recorder with a flat battery, and so does the magnetic mount holding something under a car. This is why a sweep is still worth doing when you suspect a device is not powered.
- Look for a sharp spike in one small spot. Electronics give a tight, strong reading. A steel beam or door frame gives a wide, gentle one.
- Move away and come back. If the spike returns in the same place every time, something is there.
- Check from two sides where you can. A real object reads strongly from both.
- Compare against a matching spot. Sweep the other side of the same wall, or the other seat in the car. A difference between two places that should match is the useful signal.
- Expect ordinary metal. Screws, hinges, pipes, wall studs, speakers and fridge doors all read. This is normal.
The sensor cannot tell a hidden camera from a screw. It tells you where to look with your own eyes and hands, and nothing more.
Following an infrared source
Night-vision cameras light a room with infrared. Your eyes cannot see it; a phone camera often can. Work in the dark — turn the lights off and close the curtains.
- Turn slowly on the spot, then repeat from another corner. Infrared only shows when the lens is pointing at you, so one position is rarely enough.
- When something appears, slow right down. Move one step at a time and watch whether the reading strengthens or fades.
- Walk towards it. The reading should get stronger. If it does not, you are seeing a reflection off something shiny and the real source is elsewhere.
- Look with your own eyes as well. A night-vision camera has a ring of small dark-red dots around the lens, sometimes faintly visible in a dark room.
- Start with anything facing a bed, a desk or a doorway. A camera has to see something worth seeing.
14IR Lab
A dedicated hidden-camera detector using the front camera.
Many hidden cameras use infrared LEDs to see in the dark. Those LEDs are invisible to your eye but visible to a phone camera as a faint pale glow. IR Lab turns the front camera into a viewer tuned to reveal them, with audible feedback so you can sweep a room without staring at the screen.
Calibration comes first
When you open IR Lab it calibrates against the current room. This matters: without a baseline, the app cannot tell an infrared source from ordinary reflected light, and a reading you cannot trust is worse than no reading. Verdicts are withheld until calibration completes — if the camera is blocked or the room is unreadable, the app will say so rather than reassure you falsely.
A quick self-test: point a TV remote at the front camera and press a button. You should see the emitter flash. If you do, the detector is working.
Audible sweeping
IR Lab can beep as detection strengthens, so you can watch the room instead of the screen. There is a mute control for quiet sweeps — worth using if you would rather not announce what you are doing.
Phone front cameras vary enormously in how much infrared they let through — some have strong IR filters that block most of it. IR Lab is a useful tool, not a guarantee, and it complements the lens-reflection method in Physical Sweep rather than replacing it.
15NFC Lab
Check a tracker, sticker, tag or card by touching it to your phone.
NFC is the short-range radio your phone uses for tap-to-pay. The NFC Lab uses it to read an object you hold against the back of the phone and tell you what it is. Open it from Settings → NFC Lab, or tap Read NFC on a device’s page so the result is linked to that device. It only appears on phones that have NFC.
How to read something
- Turn NFC on in your phone’s settings (the lab offers a shortcut if it is off).
- Hold the object flat against the back of the phone, near the camera, and keep it still for a second.
- The phone vibrates when it has read the tag. There is no beep, so you can check an object quietly.
What it tells you
- What the chip is — for example “NXP NTAG215, 504 bytes” — and who made it.
- AirTags and Find My items, and Samsung SmartTags in Lost Mode. Apple’s or Samsung’s own page, opened from the lab, shows the serial number and the owner’s message if they set one.
- What a sticker holds — a web link (pet ID tags, posters, business cards), text, Wi-Fi details, an app launcher or a phone number.
- Warnings worth knowing — a link that is not encrypted, shortened, uses a number instead of a name, or imitates a real website; a tag that tries to join Wi-Fi, pair Bluetooth, open an app or call a number; a blank tag anyone can program; a tag anyone can change later.
- Signs of a copied card. A real chip gives answers that agree with each other. A re-writable copy card often does not. If your own access card or key fob shows “This may be a copied card or tag”, ask whoever issued it to check it.
Nothing on a tag ever runs by itself. SentryRF only describes what it finds — it never opens a link, joins a network, starts an app or dials a number. It never writes to a tag either. You decide what to do next.
Keeping the result
Tap Add to device report. One dated line is added to that device’s notes — the chip, any copy warning and the tag’s link — and it is printed in the device’s PDF report. Notes that do not fit on the first page continue on their own page, so nothing is cut off.
What it cannot do
- It cannot search a room. NFC works only within about 3 cm — to find a hidden tracker, use Scan and the Sound Locator first, then read it here once you have it in hand.
- It does not read bank cards, ID cards or transit cards. It names them and stops.
- It cannot read pet microchips under the skin; those use a different radio that phones do not have. NFC pet tags on a collar work fine.
- It cannot detect card skimmers or readers nearby.
16Network Scan
Examining the WiFi network you are connected to.
Network Scan looks at devices sharing your local network — what they are, what services they expose, and whether anything looks out of place. It is useful for spotting an unfamiliar device on your home network, and for checking what is actually connected in a rental.
Being on your network does not make a device trustworthy. A device that guessed or was given your WiFi password is on your network too. SentryRF deliberately refuses to treat network membership as proof of safety — particularly for bare development boards, which is what most improvised surveillance hardware is built from.
17Driving Mode
Detection tuned for the road, where following looks completely different.
On foot, a device near you for an hour might be a neighbour. At 80 km/h on a motorway, a device that stays with you across kilometres is almost certainly in a vehicle behind you — random devices drop away within seconds. Driving Mode raises the weight given to that evidence.
It activates automatically once you are travelling above about 20 km/h, and stays active through stops — a tail does not stop being a tail at a red light. It disarms after several minutes of sustained slow travel. You can also open Driving Mode manually at any time.
Driving Mode only ever raises the significance of following behaviour. It never suppresses a detection, so having it active can only make the app more attentive, not less.
Vehicles
Driving Mode also recognises devices associated with vehicles. If a vehicle is your own, tag it as Vehicle and it will no longer be treated as a follower.
Automated licence-plate cameras
SentryRF recognises the radio signatures of several widely deployed automated licence-plate recognition (ALPR) systems, including Flock Safety cameras and their associated equipment, and acoustic gunshot-detection sensors such as SoundThinking Raven. These appear in your device list like anything else, labelled for what they are.
This is public infrastructure detection, not a threat assessment. An ALPR camera on a pole at an intersection is not following you and is not scored as a stalker; it is fixed equipment doing what it was installed to do. SentryRF tells you it is there because many people want to know where this equipment is deployed in the places they live and drive — the same reason you might want to know where a CCTV camera is.
Recognition is based on the exact broadcast name formats these devices emit, matched strictly. A device merely named "Flock" or "Penguin" — a speaker, a network, a toy — is not identified as surveillance equipment. If SentryRF labels something as ALPR hardware, the signature matched precisely.
What this cannot tell you. Detecting one of these devices does not mean it recorded you, that anyone is looking at the record, or that you are under investigation. It means the equipment is within radio range. SentryRF cannot read what it captured, cannot tell you who operates it, and cannot remove it.
18Map, Timeline and history
Seeing where and when, rather than just what.
Map plots where a device was detected, which is the clearest way to see the difference between something stationary and something that travels with you. Timeline shows the same history along a time axis, useful for spotting patterns like a device that only appears at night.
Threat History keeps a record of past alerts, and Scan History records the sessions themselves.
Map positions record where your phone was when it heard the device, not where the device itself is. When your phone's position is poor — indoors, in a car park — SentryRF discards the coordinate rather than saving a misleading one, so gaps in a map are honest rather than missing data.
Drones and their pilots
Most drones flown in the United States, and many in Europe, must broadcast Remote ID: their serial number, their own position and height, and the position of the pilot — or the point they took off from, depending on the drone. SentryRF reads all of it and shows it in three places:
- On the device's screen, a small north-up plot of the drone, the pilot and where your phone heard it, with the distance from pilot to drone. Tap it to open the full map.
- On the map, the drone and the pilot as separate markers joined by a dashed line. Opening the map from a drone fits all of them on screen at once.
- In the PDF report, the same plot, so it travels with your evidence.
The make and model come from the FAA's public list of declared Remote ID products, which covers about 7.7 million serial numbers. A drone that was never declared still shows its manufacturer, read from the start of its serial number. That list describes products only — never who owns a drone. Police and the FAA can link a serial number to its registered owner, which is why the serial is worth recording.
Unlike the rest of this map, drone and pilot markers show where they actually are, as broadcast by the drone itself — not where your phone was when it heard them.
19AI Core
What the on-device learning has picked up.
SentryRF runs a set of machine-learning models entirely on your phone. They learn what is normal for you — your devices, your routine, your locations — and use that to reduce false alarms and recognise genuinely unusual behaviour. AI Core visualises this and shows what has been learned.
Nothing here leaves your phone. There is no shared model, no cloud training, and no data from other users. Clearing app data resets this learning completely.
20Settings reference
The sections you will find, and what lives in each.
| Section | Contains |
|---|---|
| Scanning | Scan interval, which radios to use, scan profiles, and the optional setting that lets the app scan faster while you are moving or somewhere unfamiliar. |
| Detection | Sensitivity, which detection engines are active, and Trust familiar devices automatically (see section 6 — on by default, asked during setup), plus Detect devices moving together (off by default; see below). |
| Alerts | Notification behaviour, sound, vibration and quiet hours. |
| Safe Zones | Geofenced places where you expect familiar devices. See below. |
| Display | Home screen and scanner variants, radar style, theme. |
| Privacy | App Lock and privacy controls. |
| Data Management | Retention period, export, Remove All Trusted Devices, and Clear All Data. |
| AI & Machine Learning | On-device learning controls and reset. |
| SentryPod | Pairing and hardware configuration. |
| Driving Mode | Road-specific detection options. |
| IR Lab | Infrared camera detector. |
| NFC Lab | Identify a tag, tracker or card you touch to the phone. See section 15. |
| Help & About | Version, guides and support contact. |
Detect devices moving together
A person carries several devices — a phone, earbuds, a watch — and they arrive together. With this on, SentryRF links devices that keep travelling as one person's kit and raises an alert if that group keeps turning up where you are, away from home. Your own devices are never counted, nothing seen at home counts, and busy public places are ignored, so a family member or a crowded train is not mistaken for a follower. It is off by default while we refine it on real-world data. Turn it on under Settings → Detection if you would like the extra check.
App Lock
Under Privacy, App Lock requires your fingerprint, face or device PIN to open SentryRF. This matters in the situation the app is built for: if the person you are worried about has physical access to your phone, an unlocked detection app tells them exactly what you have been doing. If your phone has no biometric or screen lock configured, the option will not appear.
21Safe Zones
Places where a familiar crowd of devices is expected.
A Safe Zone marks somewhere like your home or workplace where a large number of known devices is normal, reducing noise from an environment you already understand.
A Safe Zone is not a blind spot. Your home is exactly where a partner, housemate or visitor is most likely to plant something, so SentryRF deliberately refuses to auto-trust trackers and surveillance hardware inside a Safe Zone. Threat assessment always runs first; the zone only quietens ordinary, established devices.
22SentryPod
Optional hardware that extends what the app can hear.
SentryPod is a handheld scanner that pairs with the app over Bluetooth or USB. Your phone's radios are designed for connecting, not for surveying — the Pod adds dedicated receivers and sensors that a phone simply does not have, and hands the raw signal to the app.
All the intelligence stays in the app. The Pod is a sensor: it detects nothing on its own, makes no decisions, and stores nothing. Pair it under Settings → SentryPod; firmware updates are delivered through the app.
23Wear OS watch
Alerts on your wrist, and a second receiver when you are searching for something.
SentryRF has a companion app for Wear OS watches. Open the Play Store on your watch and install SentryRF; the phone app must be installed too. On first open the watch asks for Bluetooth and Location, which it uses only when helping you search with Paired Sweep.
What the watch shows
The main screen shows the number of threats your phone has found, in a ring that turns orange or red as they become more serious, with the number of devices nearby beneath it. The line at the bottom shows the link to your phone: LINK ACTIVE when connected, NO PHONE LINK when not. When your phone is not scanning, the watch shows System ready.
The watch does not look for threats on its own. Everything it shows comes from your phone, so the phone needs to be scanning.
Alerts
When your phone raises an alert, the watch vibrates and shows the device, its level (Medium, High or Critical) and its score. The more serious the alert, the stronger the vibration pattern, so you can tell without looking. Tap Dismiss to clear it. To stop alerts reaching the watch, turn off Settings → Alerts → Wear OS Haptic Alerts on your phone.
The SentryRF tile
Add the SentryRF tile from your watch's list of tiles to see your threat status with a swipe. It refreshes about once a minute, and shows Open to scan when your phone has nothing recent to report.
Searching with the watch
During Paired Sweep the watch becomes a second receiver: it scans for the device you are looking for and shows its live signal, so a phone and a watch together give a sense of direction without needing a second phone. Set Settings → Alerts → Watch on right wrist if you wear it on your right, so the app places it correctly. See section 12 for how to sweep.
If it says NO PHONE LINK
- Check that Bluetooth is on and the watch shows as connected in your phone's Wear OS or Galaxy Wearable app.
- Open SentryRF on the phone. The watch rechecks the link every few seconds while its screen is open.
- If it stays disconnected, restart the watch app, then the phone app.
24Your data
What is stored, where, and how to remove it.
Everything SentryRF detects stays on your phone in a local encrypted database. There are no accounts, no login, no servers, no analytics and no telemetry. Nothing is uploaded, which is also why we cannot see your data or recover it for you.
You can verify this: turn off WiFi and mobile data completely and the app works exactly the same.
Retention and deletion
- Data older than your retention setting is deleted automatically. The default is 30 days, adjustable from 7 to 90 in Settings → Data Management.
- Clear All Data in the same section erases everything immediately.
- Uninstalling removes the entire database with the app.
Full detail is on the data deletion page and in the privacy policy.
Trial and subscription
The 7-day trial takes no card and no sign-up, so there is nothing to cancel and nothing is ever charged automatically. When the week ends the app returns to the free version. If you later choose to subscribe, that subscription is managed by Google: Play Store → Menu → Payments and subscriptions.
25Troubleshooting
| Symptom | Cause and fix |
|---|---|
| No alerts arriving | Notification permission is denied. Grant it in Android Settings → Apps → SentryRF → Notifications. On Android 13+ this also restores the scanning icon. |
| Scanning stops when the screen is off | Battery optimisation. Set the app to Unrestricted (see section 3), and check manufacturer-specific sleep lists. |
| Battery draining quickly | Increase the scan interval in Settings → Scanning. Moving from 30 seconds to 3 minutes reduces radio time roughly sixfold. |
| Hundreds of devices | Normal in flats and busy areas. Mark what you recognise as Safe and read Suspicious rather than the full list. |
| Same device appears many times | Address rotation. The app groups these automatically as it gains confidence; give it time. |
| Sound Locator will not point anywhere | Poor position quality — common indoors and in car parks. The app falls back to signal strength deliberately. Sweep slowly and follow the beep rate. |
| Physical Sweep finds nothing | Usually sweeping too fast. A few centimetres per second, close to surfaces. |
| IR Lab shows nothing | Confirm calibration finished, then test with a TV remote. Some phones filter infrared heavily at the front camera. |
| NFC Lab does not react | Check NFC is on, take the phone out of a thick or metal case, and move the object slowly across the back — the antenna is usually near the camera. No NFC Lab in Settings means the phone has no NFC. |
26What SentryRF can and cannot find
Being clear about the edges is part of being trustworthy.
SentryRF searches in two completely different ways, and knowing which is which explains almost every question about what it can and cannot find.
1. Listening for broadcasts. Most of the app uses the radios your phone already has — Bluetooth, WiFi, and the cellular receiver. This is the fast, continuous, background search, and it has one hard rule: it can only find a device that is transmitting. Silence is invisible to it.
2. Physical Sweep, which uses no radio at all. It reads the phone's magnetometer, gyroscope, light and pressure sensors, and the camera. That is how it can find electronics that broadcast nothing — a wired camera, a device powered inside a wall — because it is looking for magnetic fields and lens reflections rather than signals. It is slower, it is hand-guided, and it is the answer when the radio search comes back empty.
What the radio search finds
- Bluetooth trackers — AirTag, Tile, Samsung SmartTag, Chipolo, Pebblebee, Eufy, Google Find My, and generic beacons. These broadcast constantly by design, which is what makes them findable.
- WiFi devices — routers, cameras with WiFi, smart-home hardware, WiFi-enabled GPS trackers, and rogue or evil-twin networks.
- Bluetooth devices generally — phones, laptops, wearables, headphones, keyboards and the rest of the ordinary background.
- Drones broadcasting Remote ID, over both Bluetooth and WiFi.
- Automated licence-plate cameras (Flock Safety and similar) and acoustic gunshot sensors, by the exact names their hardware broadcasts.
- Unusual cell-tower behaviour that can indicate a fake tower.
- NFC tags and cards you touch to the phone — identified in the NFC Lab. This is a close-contact check, not a search.
What neither method can find
- Cellular-only trackers that talk directly to cell towers and never broadcast Bluetooth or WiFi. Many vehicle trackers work exactly this way. They are silent to every phone app, including this one.
- Cameras and recorders that save to a memory card and never transmit. Nothing is sent, so nothing can be received.
- Drones under 250 g — most toys and beginner models are not required to broadcast Remote ID at all.
- Devices that are switched off, or asleep between transmissions. A tracker that wakes once an hour is invisible for the other fifty-nine minutes.
- Professional equipment built to avoid detection, including anything using frequencies a phone has no radio for.
- It cannot tell you who owns a device, or why it is there. Radio broadcasts carry no owner.
- It cannot detect spyware on your own phone, or a cloned SIM. Those are software and carrier problems — speak to your mobile provider.
- It cannot see wired cameras that do not transmit, or purely optical devices. Physical Sweep helps, but nothing detects a camera that emits nothing.
- It cannot prove that something is or is not surveillance. Levels and labels are automated assessments of radio behaviour, not verified determinations.
- It cannot detect NFC card skimmers or read pet microchips under the skin.
- It cannot see most factory tyre sensors, which use frequencies a phone has no radio for.
- It cannot access anyone else's device, and does not try.
If your concern is something that might not transmit at all — a wired camera, a recorder saving to a memory card — the radio search will always come back clean, however long you leave it running. Physical Sweep is the tool for that, and your own eyes are the tool for the rest.
27If you find something
The most important page in this manual.
Think about your safety before you act. If someone placed a tracker deliberately, removing it, switching it off or moving it tells them you found it — and in an abusive situation that knowledge can escalate things quickly. Leaving it in place while you get advice is often the safer choice.
Sensible order
- Do not confront anyone based on an app reading. The app describes radio behaviour; it cannot tell you intent.
- Document it. Photograph what you found and where. If it is a tag or tracker you can touch, read it in the NFC Lab and add the result to its report — without opening any link on it. On the device's screen, Generate Report creates a PDF of its signal history, locations and timestamps — and for a drone, its serial number, the pilot's position and a map. Share Report sends the PDF together with a
.sha256file: its fingerprint and digital signature. Keep and send the two files together, because the fingerprint is what lets someone else confirm the report has not been altered. - Get advice before removing it. Domestic-violence and stalking advocates deal with electronic surveillance routinely; their help is free and confidential. In the United States, the National Domestic Violence Hotline is 1-800-799-7233. Elsewhere, a local equivalent offers the same. See our safety resources.
- Involve police if you feel unsafe. A device left in place and properly documented is often more useful evidence than one removed.
- For anything involving your phone account, SIM or passwords, start with your mobile carrier.
An app is one tool. It is good at noticing patterns you would never see yourself — and it is no substitute for a person who can help you decide what to do about them.
Questions about a detection?
Open the device in the app. Tap to see how this device was scored explains every signal behind its rating, and the Help screen covers each term. For what to do next, a domestic-violence or stalking advocate can help, and police can act on your report.
For help with the app itself, write to [email protected] — a real person reads every message. We can't assess individual detections, so please keep your reports for the people above.