A method performed by a video conference endpoint, the method comprising: transmitting an ultrasonic signal into a spatial region; transducing ultrasonic sound, including an echo of the transmitted ultrasonic signal, received from the spatial region at a microphone into a received ultrasonic signal; transforming the ultrasonic signal and the received ultrasonic signal into respective time-frequency domains that cover respective ultrasonic frequency subbands; computing an error signal, representative of an estimate of an echo-free received ultrasonic signal, based on the transformed ultrasonic signal and the transformed received ultrasonic signal by: adaptively filtering multiple ultrasonic frequency subbands of the transformed ultrasonic signal based on a set of adaptive filter coefficients adjusted responsive to the error signal individually to produce a respective estimate of the echo for each of the ultrasonic frequency subbands; differencing each echo estimate and a corresponding one of multiple ultrasonic frequency subbands of the transformed received ultrasonic signal to produce the error signal for each of the ultrasonic frequency subbands; and feeding-back the error signal to the adaptively filtering operation; repetitively computing a total power estimate based on the error signals across the ultrasonic frequency subbands overtime; detecting a change in people presence in the spatial region overtime based on a change in the total power estimates of the error signal computed across the ultrasonic frequency subbands over time; if the detecting indicates that people are present in the spatial region, issuing a command to wakeup a video camera that was previously asleep so that the video camera is able to capture video of at least a portion of the spatial region; performing face and motion detection based on video of the spatial region captured by the video camera; and issuing one or more commands to wakeup the video conference endpoint only if the face and motion detection confirms the presence of people in the spatial region. transmitting an ultrasonic signal into a spatial region; transducing ultrasonic sound, including an echo of the transmitted ultrasonic signal, received from the spatial region at a microphone into a received ultrasonic signal; transforming the ultrasonic signal and the received ultrasonic signal into respective time-frequency domains that cover respective ultrasonic frequency subbands; computing an error signal, representative of an estimate of an echo-free received ultrasonic signal, based on the transformed ultrasonic signal and the transformed received ultrasonic signal by: adaptively filtering multiple ultrasonic frequency subbands of the transformed ultrasonic signal based on a set of adaptive filter coefficients adjusted responsive to the error signal individually to produce a respective estimate of the echo for each of the ultrasonic frequency subbands; differencing each echo estimate and a corresponding one of multiple ultrasonic frequency subbands of the transformed received ultrasonic signal to produce the error signal for each of the ultrasonic frequency subbands; and feeding-back the error signal to the adaptively filtering operation; adaptively filtering multiple ultrasonic frequency subbands of the transformed ultrasonic signal based on a set of adaptive filter coefficients adjusted responsive to the error signal individually to produce a respective estimate of the echo for each of the ultrasonic frequency subbands; differencing each echo estimate and a corresponding one of multiple ultrasonic frequency subbands of the transformed received ultrasonic signal to produce the error signal for each of the ultrasonic frequency subbands; and feeding-back the error signal to the adaptively filtering operation; repetitively computing a total power estimate based on the error signals across the ultrasonic frequency subbands overtime; detecting a change in people presence in the spatial region overtime based on a change in the total power estimates of the error signal computed across the ultrasonic frequency subbands over time; if the detecting indicates that people are present in the spatial region, issuing a command to wakeup a video camera that was previously asleep so that the video camera is able to capture video of at least a portion of the spatial region; performing face and motion detection based on video of the spatial region captured by the video camera; and issuing one or more commands to wakeup the video conference endpoint only if the face and motion detection confirms the presence of people in the spatial region.