Abstract: Among multiple surveillance devices for mechanical security monitoring provided in a security system using sensors at least one of the multiple surveillance devices is equipped with a receiver for receiving standard time data and the standard time data received by the receiver is sent over a distribution line to required surveillance devices not equipped with receivers. This enables highly accurate time calibration among the multiple surveillance devices for mechanical security monitoring to be efficiently achieved using a power-line carrier (PLC) technology and, as such, allows sharing of accurate time data among the surveillance devices.

Abstract: In a security system using sensors that includes clock-equipped surveillance terminals for sending security data to a surveillance center, one surveillance terminal uses a power supply line to send a time calibration signal to the other surveillance terminals at appropriate times, the surveillance terminals use the signal to eliminate time error among their clocks, the other surveillance terminal use the power supply line to send to the one surveillance terminal time-stamped data, and the one surveillance terminal discriminates operating states of the other surveillance terminals by comparing the receive time and send time of time-stamped data.

Abstract: In a security system using sensors that includes clock-equipped surveillance terminals for sending security data to a surveillance center, one surveillance terminal uses a power supply line to send a time calibration signal to the other surveillance terminals at appropriate times, the surveillance terminals use the signal to eliminate time error among their clocks, the other surveillance terminal use the power supply line to send to the one surveillance terminal time-stamped data, and the one surveillance terminal discriminates operating states of the other surveillance terminals by comparing the receive time and send time of time-stamped data.

Abstract: Among multiple surveillance devices for mechanical security monitoring provided in a security system using sensors at least one of the multiple surveillance devices is equipped with a receiver for receiving standard time data and the standard time data received by the receiver is sent over a distribution line to required surveillance devices not equipped with receivers. This enables highly accurate time calibration among the multiple surveillance devices for mechanical security monitoring to be efficiently achieved using a power-line carrier (PLC) technology and, as such, allows sharing of accurate time data among the surveillance devices.