(01.03.2018)

Think of 32 kHz as the station’s frequency. When the 25 kHz tone interferes with the transmission, audible sound at 7 kHz results. The researchers also built a proof of concept device to simulate covert eavesdropping by playing a song instead of the 180 Hz tone over the 32 kHz ultrasonic carrier.

Ultrasound emitters are all around us. They can take the form of room occupancy sensors in energy-efficient buildings, rodent repelling devices, burglar alarms, security cameras, and HVAC system vibrations.