Sonar is used to track in-room activity. A sonar device provides acoustic location and tracking of multiple objects that are co-present in a room. A sender/receiver in the sonar device directs a sound wave toward the multiple objects and collects the reflected sound waves from the multiple objects over multiple time intervals. The echo characteristics of the co-present multiple objects in the reflected sound waves collected over the multiple time intervals are differentially analyzed to determine the locations of, and track movement of, individual objects of the multiple objects.
Wu, Honglei, "Differential Sonar", Technical Disclosure Commons, (October 24, 2017)