he Kidde 44200702-N is a 9V battery powered smoke alarm. This smoke alarm functions as a single unit smoke alarm and features Hush®, allowing you to quickly silence nuisance alarms. The 44200702-N is easy to install, no wiring is required. This smoke alarm combines both photoelectric and ionization sensors. Ionization sensing alarms may detect invisible fire particles (associated with flaming fires) sooner than photoelectric alarms. Photoelectric sensing alarms may detect visible particles (associated with smoldering fires) sooner than ionization alarms. Kidde strongly recommends that both ionization and photoelectric smoke alarms be installed to help insure maximum detection of the various types of fire that can occur within the home.