Android Beacon Library: Keep BeaconTransmitter running "forever"

Question

is there any way to keep a BeaconTransmitter instance sending forever?

The Problem: I want a RPi detect when I am coming home independent of Wifi running or the RPi even having access to the internet (e.g. it could then turn on all routers etc., when it detects the phone).

I have a minimalistic app on my android phone sending out an iBeacon running and the beacontools Library on the RPi detects it. This is working well, in principle. (Although I know it's supposed to be the other way around, but I again, I want the RPi to be able to do "stuff" without having access to the internet, what the phone cannot do).

However, the power management(?) on the Android phone seems to stop the transmission, the latest after a few hours (even if the App is "not optimized" for battery usage). I am not even sure if this is because of the battery optimization or something else.

Solution so far: I am using a PeriodicWorkRequest that checks every 30 minutes (I read somewhere this is the minimum time), if the beacon is still running and relaunches it, if it is not.

This also works as expected, but of course, I keep coming home in the time slot when the beacon transmission has stopped and before it is kicked off again by the WorkManager. ;)

A cleaner way would be to "intercept" when the BeaconTransmitter is killed by PowerManagement/BatteryManager(??) or something. Is that possible? Those covid tracking apps are using something (I hope) that ensures continuous transmission, but I know that Google/Apple had to implement something fundamental to allow those to work, and of course, I cannot use the covid-tracking itself because it is anonymous by design.

Answer 1

A precise answer will vary by phone manufacturer as many OEM's fork Android to kill long-running apps in the background. See here for a summary of challenges by OEM.

For vanilla Android (Pixel phones, many Nokia Android Once devices), Motorola and even most Samsung devices, it is sufficient to keep a foreground service active and have Location always runtime permission. My BeaconScope app uses this foreground service technique, and I typically see a transmitter keep going for weeks on a Pixel or Samsung device. Be sure you grant "Always" location permission to the app for this to work.

You can see the code needed to set up the foreground service in the Kotlin reference app for the Android Beacon Library. The comments indicate that the foreground service is useful for continuous beacon scanning, but it is equally true that it is useful for long-term beacon transmission.

Without the foreground service, the beacon transmission will only last about 10 minutes after the app is put to the background on vanilla Android, at which time the app will be killed.

The problem with a periodic work request or a job service is that they can run at most every 15 +/- 10 minutes on Android. So if the transmitter is killed every 10 minutes you will end up with gaps of up to 15 minutes without transmission. On Android 8+ you have no choice but to use a foreground service.