Another scenario, leave it in an isolated hut. If I get a signal, someone is close to the hut.
You could do that already with a device, just by making an app that listens for Bluetooth or WiFi traffic. You’d also be able to grab MAC addresses of the nearby phones. Your ‘exploit’ isn’t revealing any more than you can already discover today.
If there’s internet connectivity, and you’re sophisticated enough to be planning Find My iPhone based booby traps, firing off a text message from a contained detector shouldn’t be a challenge
You could do that already with a device, just by making an app that listens for Bluetooth or WiFi traffic. You’d also be able to grab MAC addresses of the nearby phones. Your ‘exploit’ isn’t revealing any more than you can already discover today.