This Smartwares RM250 Smoke Detector is equipped with an optical sensor and is CE and TUV certified. An optical sensor reacts quickly to smouldering fires and has less false alarms than other types of smoke detectors. The RM250 Smoke Detector has a 1 year battery meaning you must replace it every 12 months. The optical sensor of the smoke detector has a 10 year lifetime after which time you need to replace the whole unit. At 10cm in diameter, this smoke detector can be placed discretely in key locations and should a fire be detected, the alarm will sound at a loud 85 decibels.