Patent ID: 7242297

Claim:
A sensor for use in an alarm system to monitor movement of an object and to place the system into alarm when the object moves more than a predetermined distance from a predetermined position comprising: a first reed switch and a second reed switch, both reed switches being located in a predetermined orientation relative to each other and to the object; bias means comprising a first magnet for the first reed switch and a second and separate magnet for the second reed switch; and, force means including a third magnet which is movable with the object and produces a force simultaneously sensed by both reed switches, said third magnet and said first and second magnets together producing a null field for each of said first and second reed switches when the obiect is in a predetermined position, and said force means maintaining both reed switches in a state which maintains the alarm system in a non-alarm condition so long as the object substantially remains in its predetermined position, but movement of the object more than the predetermined distance resulting in the force means increasing its force sensed by one of the reed switches and decreasing its force sensed by the other reed switch, either of which conditions causes the alarm system to go into alarm.