To reduce the cost and to attain compactness of a device to be monitored by detecting the frequency of a magnetic body which receivers incident magnetic field radiated inside a monitor area and generates a specified frequency and issuing alarm.
The monitor area is formed in the neighborhood of an entrance/exit by radiating electromagnetic wave from the transmitting antenna 12 of a monitor device mainbody 1 at all tomes. At the time of entering the monitor are in a state of fitting the device to be monitored 8 to commodity 15, the magnetic body of a sensor part 9 in the device to be monitored 8 receives electromagnetic wave from the transmitting antenna 2 and a high harmonic is emitted by a large Barkhausen effect. The electromagnetic wave is received by the receiving antenna 4 and the receiver 5 of the monitor device mainbody 1 and the alarm means 7 of the monitor device main body (gate part) 1 issues alarm when the signal is more than a stipulated value. When the magnetic body received electromagnetic wave, a pulse-shaped voltage is generated at the both ends of a coil part in the sensor part 9. The signal of the specified frequency is amplified in an amplifier part 10 and the alarm means 12 of the device to be monitored 8 issues alarm at the time when the signal has more than a stipulated value.
ICHINOMIYA NOBUYUKI
SUZUKI TAKASHI
NIIMURA SHIGERU
MIYAKE HIDEKI
ARIMOTO HIDEKI
SECOM CO LTD