This clearly eliminates the need for battery changes. As far as we can tell, there are no AC powered smoke alarms currently made with dual sensors, and one reviewer suggests using both photoelectric and ionization alarms in the same location. Most models such as these that use house wiring for power are also equipped with a battery backup in case of a power failure. Most, but not all, models do. Units should have a test button to ensure that alarms and sensors are operating correctly.
Photoelectric sensors sound when the smoke is dense enough to deflect a beam of light.
All fire detectors have a unit life of about ten years, experts say. So it's important to replace old units each decade. Units that use nine-volt batteries need to have fresh batteries each year. Reviewers say an easy way to remember to replace the batteries is to do so at the start of Daylight Savings Time each year. Our Consensus Report shows how many times products are top-ranked by reviewers included in our All The Reviews Reviewed chart.