Awareness and alerting is all well and good
But I want something that emits an EM field that will cause a mic to record some gawd-awful feedback without being picked up by Mk1 Earballs (Much like shining an IR light into a camera). This would also be useful for the voice-operated "smart" TVs that are absolutely not spying on you. Bonus points if the EM field would not effect hearing aids.
I would also accept if the EM field just generated white noise, but I would love either a 15KHz tone, or failing that, Rick Astley's "Never Gonna Give You Up"