For the smoke detection the unit includes ionization sensing technology, which detects visible fire particles and warns of impending danger. The carbon monoxide alarm goes off if the carbon monoxide levels in your home increase to a dangerous level. The Kidde KN COSM B Battery Operated Combination Monoxide has four verbal warnings including fire, carbon monoxide, low battery and smart hush announcement. There is a voice alarm, a flashing light, along with a loud beeping sound that warns of danger. 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.