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Ultrasonic beacons: https://www.schneier.com/blog/archives/2017/05/using_ultrasoni.html https://www.schneier.com/blog/archives/2017/05/using_ultraso...
by smokeyj 9y ago
Ultrasonic beacons: https://www.schneier.com/blog/archives/2017/05/using_ultrasoni.html https://www.schneier.com/blog/archives/2017/05/using_ultraso...