A PIR system is a passive infra-red sensor which measures infra-red light. They can be used as part of a security system to detect intruders and send out an alert in order to keep buildings protected. They’re a useful way of monitoring motion and are highly accurate.
It’s important that you consider carefully where you are going to put a PIR system. They aren’t suitable for use out of doors as they might be set off by animals or people walking past a building. In order to avoid false alarms, they will need to be placed somewhere where they’re not going to pick up any other kind of motion. If they’re being placed by a window, consider whether they could still pick up any motion from out of doors. The devices will have a clearly-marked radius for its beam, so it might be worth checking this.
The devices are usually easy to install and to integrate with an alarm system. They tend to be wireless, making the process a lot easier. You might also have the option to choose a model with an auto dialler, which will call a pre-set number if any unexpected motion is detected.