Seems solvable in this case. Ultra-sound can wake up the device, but then it would take some other signal to have it do anything other than go back to sleep, li

Seems solvable in this case. Ultra-sound can wake up the device, but then it would take some other signal to have it do anything other than go back to sleep, like WiFi/Bluetooth/LAN/etc.. So you wouldn't get incorrect functionality triggering from accidental ultra-sound triggers, you'd just save less battery.