then de energizes the relay to stop the supply of electric charge next if the activation time is the routing participation time the sensor unit 110 energizes the relay 106 in the case of the sensing time or the routing start time the sensor unit de energizes the relay 106 the sensor unit next de energizes the relay 103 to stop the supply of power from the power source 107 to it the wireless sensor is thus placed in the standby state a description is given below of the operation of each component when the wireless sensor goes from the standby state into the activated state as described above the high sensitivity rectifier 102 converts a radio signal received by the antenna 101 into electric power by energizing relay 103 therefore the supply of power from the power source 107 to the sensor unit 110 can be started however trying to control the relay 103 with the high sensitivity rectifier 102 alone would cause a wireless sensor which is not associated with the routing path to be activated by a radio signal from a surrounding wireless sensor this is because the rectifier converts a radio signal received by the antenna 101 into electric power regardless of its contents for this reason the wireless sensor of this embodiment is configured to incorporate a logic circuit into the high sensitivity rectifier 102 so that the rectifier energizes the relay 103 only when timer runout occurs the logic circuit can be readily formed using an xor or and circuit and.