The optical smoke alarm is the ideal replacement for ST-622 or ST-620 smoke alarms. No need to replace the base plate.
The optical design will provide early fire detection, ideal for slow burning fires.
With a large central button for easy testing. 1 push activates a quiet self test whilst 2 pushes activates the full volume test.
These alarms require 2 x AA batteries to operate which will last for 5 years before needing replaced.