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.

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Then 9/11 happened and suddenly we have Wi-Fi and Bluetooth competed with infrared before it dominated. Bluetooth’s wlan not getting good is still sad to me.