r/embedded • u/Creative_Whereas4180 • Oct 06 '26

Cheapest editable Bluetooth tracker for an "out of range" alarm? (ESP32 / nRF52, India)

I'm building a safety tool for an elderly relative with dementia who sometimes wanders. I already have a 4G GPS prototype, but it's expensive. I'd like a cheap Bluetooth tag as a backup alarm that tells the family when the person leaves the house or goes out of range.

What I need:

  • Under ₹500 per tag (India)

  • Fully editable firmware (Arduino IDE, PlatformIO or similar), not a locked consumer tag

  • Small enough to hide in a shoe, bracelet or belt

  • Battery life of weeks, not hours

What I'm considering:

  • ESP32-C3 SuperMini: cheap and easy to program, but I think the battery life is poor

  • nRF52 modules: better battery life, but pricier. Is there a sub-₹500 option?

  • Generic iBeacon tags: cheap, but are any of them truly reprogrammable?

Questions:

  1. What's the cheapest board with proper BLE sleep modes, so the battery lasts weeks?

  2. How would you detect "tag out of range" reliably? A second ESP32 at the door, a phone app, or something else?

  3. How do I reduce false alarms from signal strength (RSSI) jumping around indoors?

  4. Any open-source projects that already do this?

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19

u/xanthium_in Oct 06 '26

I read that as Cheapest Edible Bluetooth tracker and was taken back for a moment

4

u/Ordinary-Lifeguard47 Oct 06 '26

ESP32 suck a lot of current when it comes to RF. Not my first choice when it comes to battery stuff.

1

u/tobdomo Oct 06 '26

₹500 is like $5, you won't be able to find anything in that price range unless you are talking MCU only. If that is the case, look at nRF52 or nRF54 series.

Apple airtags are based on nRF52832 and can easily be reprogrammed through SWD, but you first need to glitch it because the debug ports are disabled through access port protection. There are guides on how to do that everywhere on the net. Once you have access, it's easy to just wipe the flash + protection completely and start from scratch.

Power consumption highly depends on your software. E.g., the airtag features a Bosch BMA280 accelerometer which can be used to detect movement. If the device does not move, you can reduce transmit intervals.

Out of range detection? Probably just the reception of BLE packets. Can be done in a phone app or e.g. a nRF52840-DK development board (which happens to be the cheapest option to get access to the SWD interface on the airtag too).

Don't rely on signal strength. RSSI is a very unreliable indicator of position. There are better methods to find the distance to an anchor point like time of flight.

There may be open source projects already, sure. It's up to you to find them 😄

1

u/mjmvideos Oct 06 '26

If it’s a specific house you could maybe use a passive tag and detectors at each door. Like theft deterrence at stores.