The First Alert SA320CN Double Battery Powered smoke detector has a loud alarm so it can be heard throughout the house and responded to quickly. Rest at ease, and have the peace of mind that your home is protected with the First Alert SA320CN Double Battery Powered smoke detector. It comes with a 10 year warranty. The First Alert operates with AA batteries and should be checked twice a year for battery life. The Kidde KN COSM B Battery Operated Combination Monoxide detector is a combination smoke and carbon monoxide detector. Carbon monoxide is an odorless and tasteless gas that can kill residents even when low amounts are inhaled. Instead of having both a carbon monoxide detector and a smoke detector, this unit combines the two into one unit. 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.