A motion sensing system device and method which utilize dispersed ultrasonic
radiation
is disclosed. The system preferably comprises a low profile sensor unit configured
to couple to a ceiling position. The sensor unit comprises an ultrasonic transmitter
and an ultrasonic receiver and a pair of acoustic reflectors positioned in a transmitting
path of the ultrasonic transmitter and a receiving path of the ultrasonic receiver
for generating and detecting the ultrasonic radiation in a broadcast field. The
acoustic reflectors preferably comprise cones, conical cross-sections and/or combinations
thereof which are integral with the ultrasonic transmitter and the ultrasonic receiver
and/or are coupled to a housing structure for positioning the acoustic reflectors
in the transmitting and/or receiving paths. The sensor unit also preferably comprises
a circuit for driving the transmitter and for detecting motion by detecting changes
in the receiver signal. In further embodiments, the system also includes an infrared
sensor and is configured to generate a response based on the combination of changes
in the receiver signal and a signal form the infrared sensor.
