Detecting Motion Based on Repeated Wireless Transmissions

In a general aspect, motion of an object is detected based on wireless signals. In some aspects, wireless signals based on a repeated wireless transmission are received at a wireless sensor device in a space. The received wireless signals are analyzed, by operation of a processor, to detect movement of an object in the space. The analysis includes determining complex values representing the relative phases and amplitudes of respective frequency components of each of the received wireless signals, and detecting movement of an object in the space based on a change in the complex values.