CMS
An installation of a security system without interconnection to a Central Monitoring Station (CMS) and only using a siren does not only constitute any serious security operation. The CMS allows on a 24-hour basis the complete monitoring of the protected area as well as possible problems (e.g. power failure that remains for very long time) that will have to be checked.
Other choices are the use for panic, medical help but even the monitoring of refrigerators and freezers in shops with use of relative sensors.