Вот контекст:
Most intruder systems have a combination of perimeter and trap protection.
· Trap protection is used to describe those devices activated once the intruder is within the perimeter. This form of detection relies upon the identification of movement and/or body heat. Modern dual technology detectors rely on the identification of both before an alarm is signalled. Although these units are more expensive they are more reliable and subject to fewer false activations.

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Можно еще из той же серии:
выражение: "alarm company"
контекст:
They then transmit an alarm over a telephone line to the fire brigade, or more often to an alarm company’s receiving centre as well as causing a local alarm to initiate an evacuation of the premises.