Combination photoelectric smoke & electrochemical carbon monoxide sensors detect deadly smoke, fire & CO hazards Patented smoke entry system allows for a direct path to the photoelectric smoke sensor Nuisance-free photoelectric technology reduces false alarms that result from cooking & shower steam New, thin design adds an element of style Meets UL217 & UL2034 standards & complies with legislative requirements for 10-year battery operated smoke alarms Powered by sealed, 10-year lithium batteries