警报和安全系统是有用的，但提供很少的保护或决定由经验丰富的入侵者。
Alarms and security systems are helpful, but provide little protection from experienced or determined intruders.
当入侵者企图进入，警报条件就会被触发，从而提醒保安人员并指出其事发地点。
When an intruder attempts to gain access, an alarm condition is triggered that alerts security personnel and indicates where the incident took place.
入侵者通过屏障时会干扰红外光束，从而触发警报接触，使得他们被发现，而自己却不知情。
Intruders passing through the barrier break the beams and trigger an alarm contact, causing their presence to be detected without their knowledge.
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