Go into developer mode on your android and you can toggle see hidden Bluetooth devices. Anyone can see all the by devices around them same with wifi. Jamming them is a federal offence; Logging them and Scanning them isn't.
Anyone can make a jammer or buy one off of aliexpress at your own expense, I stay away from them even though I've been tempted to build one. Alas, I'd rather read about people who do, than be the one who did.
