Devices programmed as silent alarms do not trigger external alerts when activated. What is this device type?

Silent alarms are specifically designed to alert security personnel without drawing attention to the alarm itself. They do not trigger external alerts, ensuring that unauthorized individuals are unaware that an alarm has been activated. This feature is crucial in situations where alerting the perpetrator could lead to escalation or violence.

The device type identified as a silent alarm corresponds with the classifications used in security systems. Type 22 typically refers to devices that operate in this discreet manner, designed for situations requiring covert response and minimizing risk to individuals or property. The focus on silence and discretion aligns with the need for security measures that are effective without providing immediate notification to an intruder.

Other types mentioned in the question may serve different functions or trigger alerts that are audible or visible to the environment, which does not fit the requirements of a silent alarm.