| 摘要 |
PURPOSE: To improve operability by always transmitting an existence indicating signal by a transmitter other than the time of transmitting an unlock signal, holding the unlock state in the case of receiving after unlocking, and locking when the receiving electric field strength of the existence indicating signal is lower than a predetermined level. CONSTITUTION: One terminal of an unlock switch 4 is connected to the positive electrode of a battery 3, and the other end is connected to a transmission control circuit 2 through a line 11, whereby only when the unlock switch 4 is pressed, an unlock control signal output from the circuit 2 is given through a line 12 to a transmit circuit 5. When the unlock switch 4 is not pressed, always an existence indicating signal is given through the line 13 to the transmit circuit 5 to hold the unlock state as far as the existence indicating signal is received from a transmitter by a receiver in the unlock state, and only when the electric field strength of the existence display signal is lowered than a predetermined level, automatically locking is performed. Thus, it is possible to prevent the transmitter from being confined in error. |
