As Outside Magazine notes, enterprising thieves have been using Bluetooth scanner apps – particularly in otherwise deserted areas like trailheads – to quickly scan their surroundings for high-value targets. To avoid this fate, simply put your device into Airplane mode (Android, iOS), turn it all the way off or, of course, avoid having to leave it in the car in the first place.
Better yet, you can test your own preventative measures by downloading a readily available Bluetooth scanner app yourself to see if your devices are visible by this method even after you have attempted to disable them. Certain devices like wireless headphones and fitness trackers can be pretty insistent on sending out Bluetooth signals for pairing purposes, so it is worth double-checking you actually know how to disable them fully.
Or, for a dead-simple approach that will cost you a few bucks, pick up a signal-blocking “Faraday bag” to keep in your car, so you can be sure the gadgets inside it can’t signal the outside world no matter how hard they try.