| 摘要 |
A simply installable, economical, room of a motel or hotel unit is provided in each room and an electrical device to be protected is connected to the room unit without the need for any modification of the device. The room unit is of sufficient sensitivity to sense various conditions indicative of an attempted theft, including the difficult to sense condition of cutting the power cord of the electrical device when the device is off. Each room unit is responsive to the detection of a condition indicating an attempted theft to produce a unique alarm signal which is coupled back to the AC power lines. The power supply lines of a plural phase AC power system customarily provided in the hotel or motel are used to transmit the alarm signals from the room units to receiving means for detection, and spare telephone lines which are customarily also available are used to transmit the detected alarm signals from the receivers to a central monitoring location. A vibrating reed system employing piezoelectric reeds as the frequency controlling elements as well as the driving and sensing transducers is used in the room units and in other portions of the system for providing highly stable tuning of oscillators and filters.
|
