31 Smart Sensors and Sensor Networks Examples Smart sensors:  Cricket sensors: RF sensors; Ultrasonic sensors; Tiny OS; Powered with batteries or externally; RS232 interface for being programmed or transferring data; 2 modes:  Beacon,  Listener; The time difference between the RF pulse and the ultrasonic pulse indicates the distance among a beacon and a listener; Applications: space identifiers and position coordinates: the beacons are deployed in a delimited space and they will indicate the position of one or several mobile listeners;
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