In simple terms, according to the different power supply methods, we can divide the smoke detector into the following two types
Here are two kinds of smoke detectors（please click here to the sealed smoke detector we recommend）: SR-853
Battery-operated type: These cheap units can easily be installed anywhere. They require frequent inspection to makesure the condition of the battery.（sealed smoke detector we recommend is the type）
AC-powered type: Installed by an electrician (or those with a good working knowledge of electricity), these units are much more dependable over the long haul due to their direct-wired power source. But we recommend that they should have an independent battery （like sealed smoke detector）backup so that they continue to operate during a blackout or an electrical fire that temporarily interrupts power.
For minimum coverage, You have at least one smoke detector or alarm on every level of your house and in every sleeping area. （sealed smoke detector is very popular for nowdays）meantime, you can also add other fire alarms to hallways outside every bedroom, the top and bottom of all stairways, and often-forgotten places such as utility rooms, basements, attics, and garages.