The Kidde KN COSM B Battery Operated Combination Monoxide alarm needs 3 AA batteries to operate and comes with a 5 year warranty. Photoelectric smoke detectors can detect slow, smoldering smoke the fastest, like the thick smoke when a couch or mattress is one fire. In comparison to smoke detectors using ionization technology, photoelectric smoke detectors set off an alarm earlier on slow burning materials. It can detect smoke faster in a large area or in a room with a high ceiling or rooms subject to temperature extremes. On the other hand the ionization type smoke detector is more sensitive to flames than to smoke. It sets off an alarm faster than a photoelectric or optical beam smoke detector once it detects fire. Therefore it is best used to detect smoke from fast flaming materials like paper and wood. It is also cheaper to manufacture. Compared to photoelectric smoke detectors, it consumes less power so a small battery can power it for month and is independent of external wiring. Since ionization type smoke detectors can detect particles smaller than smoke particles, they are prone to false alarms. Ionic smoke detectors use a radioactive isotope americium 241, and rules on proper disposal vary in each region.