Meshtastic is awesome, everyone go play with it, it's getting more accessible by the day.

There's a lot you can do on the hardware side. A device with three BLE chips supporting the appropriate modes would be able to sniff all three advertising channels at once, greatly increasing acquisition speed. High gain directional antennas would massively increase range. If you were especially squirrelly you could build in a GPS with high precision timing (~$25-100) and geolocate the packets via MLAT (https://en.m.wikipedia.org/wiki/Pseudo-range_multilateration). Moving up to a GPSDO you could start to do things like determine the speed and direction of travel of the sender.

In practice it's usually at or more commonly under 100m. Since we're at the mercy of what Axon has graciously provided for us, were unlikely to get BLE long range (coded PHY) type packets out of these devices, they probably have no use case for supporting the extension.

Yup, that's it. BLE Radar is the best app I've found so far. Someone go make a PR for playing a sound when a profile matches though...

Tasers, bodycams and holsters among other things made by Taser are constantly spamming advertising packets over BLE in order to be able to link to each other quickly (ie if a taser or gun is drawn, turn on the body cam). These devices are almost all made by one company and per the Bluetooth specification, the manufacturer ID is the first three bytes of the device ID, 00:25:DF: the address for Axon International Torture Devices.

Credit to Nullagent/rfparty for discovering the vulnerability. https://www.engadget.com/how-hackers-are-using-bluetooth-to-track-police-activity-140012717.html

A couple notes in practice: without dedicated hardware BLE advertising packets are very random, your phone can only sense one of the three advertising channels at once and it rotates though them. Additionally local band conditions (how many innocuous BLE devices are also around, WiFi, unrelated ISM stuff, other factors) can change sensitivity. BLE is a chaotic spammy protocol that likes to shout over itself. As a result, detections can happen the instant someone gets within ~100m of you, or they may not be detected for several seconds. Some departments may not even use Axon hardware at all, though the majority seem to. You may be able to use the WiGLE database to get a sense for your locale, but I haven't dug into that yet.

Further research: This has a lot of potential for protest/protected first amendment activities. As stated, the ability to cue an audio alert. Apps that can trigger audio/video recording when cops are very close (high RSSI). Apps that can alert a friend that lots of cops are very close and the user is unable to halt a countdown. Apps that can wipe/lock/turn off a phone if lots of cops are very close or around for an extended period of time (in custody).