An intrusion detection system senses entry where none is allowed. Door contacts, motion sensors, glass-break detectors and shock sensors report to a panel, which arms and disarms by area and sends an alert. The design job is reducing false alarms without missing a real entry.
Detection is the layer that reports a break-in attempt, while access control decides who may enter. The two are often installed together and should share a plan.
The sensors that do the work
Contacts watch an opening, passive infrared sensors watch a volume for body heat, and glass-break sensors listen for the frequency of shattering glass. Each covers a different failure.
Arming, zones and alarms
The panel groups sensors into areas that arm independently, so a stockroom can be armed while the sales floor trades. Alerts should have two independent paths.