| 摘要 |
An improvement in Instrusion Alarms of the type wherein a field wire acts as a transmitting antenna to produce an electric field and wherein a sense antenna is placed in the vicinity of the field wire to detect an intruder wherein at least one pair of field wires are employed at the extremities of a vertical configuration with sense wires between the field wires. The movement of a large object in the vicinity of such a system produces an equal perturbation on both of the sense wires so that no alarm is set off while an actual intrusion will cause a difference which is detected and utilized to provide an alarm system which is less susceptible to false alarms than the usual alarm systems.
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