Using the sensing technology of choice for the UK's Fire & Rescue Service the Fire Angel ST-623 is an alkaline battery powered smoke alarm featuring an ultra bright LED. The escape light is designed to provide a reference point within an escape route in the event of a fire. with a test & hush button feature as well as specially designed "sleep-easy" function to temporarily silence low battery or end of life warning chirps for 8 hours.ï ½ 5 year warranty.