Self contain Optical Smoke detector and alarm sounder, Sound level 80dB, Detection Area 40m2. SMOKE ALARMS VS. SMOKE DETECTORS: Often you hear people using the terms smoke alarms and smoke detectors interchangeably. However, there is a difference between the two. What’s the difference? A smoke alarm is an all-in-one, self-contained device, with a detector, which senses the products of combustion (smoke) and sounds an audible, and sometimes visual warning or alarm. Smoke alarms are widely used in residential settings. Put simply, a smoke alarm detects smoke and sounds an alarm. A smoke detector is strictly a sensing device only, which senses the products of combustion (smoke) and sends a signal to a building’s fire alarm system to activate an audible, and sometimes visual warning or alarm. Smoke detectors must be connected to a building’s fire alarm system and are NOT a stand-alone unit. Put simply, a smoke detector senses smoke only and must be connected to a fire alarm system control panel. Smoke detectors are a detection device only – not an alarm.