A fire alarm with NO automatic detection such as smoke or heat detectors.
It has only manually operated "break glass" units for persons to raise alarm.
A mains powered central control panel with battery back up and sounders are still required.
The minimum decibel level should be 65db throughout the premises.
Design, installation & commissioning certification is required for the system in accordance with BS5839pt1 (2002).
Hope that helps.
F3