This protective cover has been helping stop malicious and accidental false fire alarms around the world for over 40 years, without restricting legitimate alarms. This version of the Stopper II has a four inch deep enclosed back box which allows it to be installed in wet or wash down areas (such as kitchens, cafeterias, meat packing plants, showers, outdoors, etc.). It helps protect against physical damage (both accidental and intentional), dirt and grime. The enclosure is not locked which makes it easy to open for legitimate operation.