Patent ID: 7761212

Claim:
A wireless communication apparatus comprising: a master unit comprising: a master unit transmitter configured to transmit a beacon periodically; and a master unit receiver; a detector configured to output a detected signal; and a slave unit configured to receive the detected signal from the detector, said slave unit comprising: a slave unit receiver configured to receive the beacon periodically at a receiving timing determined based on the beacon; and a slave unit transmitter configured to transmit the detected signal to the master unit receiver at a transmitting timing determined based on the beacon if a value of the detected signal changes by a threshold amount, wherein: the master unit receiver is configured to receive the detected signal transmitted by the slave unit transmitter; the master unit transmitter is configured to transmit a confirmation signal in response to receipt of the detected signal by the master unit; the slave unit receiver is configured to receive the confirmation signal transmitted by the master unit transmitter; and the slave unit is configured to enter a sleep mode after receipt of the confirmation signal.