Abstract: An ultrasonic-based person detection method. The method comprising the steps of: (a) emitting, from an emitter, an ultrasonic signal, the ultrasonic signal including a component at a first frequency; (b) receiving reflections of the ultrasonic signal, the received signal including components at frequencies greater than and less than the first frequency; (c) determining a difference between an upper portion of the received signal containing a frequency higher than the first frequency, and a lower portion of the received signal containing a frequency lower than the first frequency; and (d) determining, based on the difference between the upper portion and the lower portion, whether a person is present.

Abstract: An ultrasonic-based person detection method. The method comprising the steps of: (a) emitting, from an emitter, an ultrasonic signal, the ultrasonic signal including a component at a first frequency; (b) receiving reflections of the ultrasonic signal, the received signal including components at frequencies greater than and less than the first frequency; (c) determining a difference between an upper portion of the received signal containing a frequency higher than the first frequency, and a lower portion of the received signal containing a frequency lower than the first frequency; and (d) determining, based on the difference between the upper portion and the lower portion, whether a person is present.

Abstract: An endpoint among a plurality of endpoints, synchronizes a clock across the plurality of endpoints. The endpoint generates a received ultrasonic signal by transducing ultrasonic sound received at a microphone from a spatial region. The ultrasonic sound includes an identical ultrasonic signal transmitted from the plurality of endpoints and echoes from the spatial region. The identical ultrasonic signal is generated with respect to the synchronized clock. The endpoint computes an error signal based on removing the identical ultrasonic signals and the echoes from the received ultrasonic signal. The endpoint detects motion in the spatial region based on a change in the error signal over time.