This protective cover has been helping to stop false fire alarms around the world for more than 30 years, without restricting legitimate alarms. All models offer excellent protection against physical damage (both accidental and intentional) and several against severe environments both inside and out. It is ideal for schools, colleges, hospitals, nursing homes, stores, hotels and public buildings of almost every kind where there is a threat of false alarms.HOW IT WORKSStopper II consists of a clear, tamperproof, tough polycarbonate shield and frame, but the line includes models with the option of a piezo horn, spacer, Form "C" dry relay contact and gaskets. The cover accommodates most manual pull stations. When the Stopper II with horn is lifted to gain access to the protected alarm, a piercing self- contained 95 or 105 dB warning horn (at one foot) sounds. Immediate attention is drawn to the area and a prankster will either run or be caught. The cover is connected to the frame by a cable. When the cover is lifted, it drops off of the frame and a horn will sound (models with horn) until the cover is snapped back onto the frame or for the life of the battery.