describe This type of smoke and carbon monoxide detector uses electrochemical carbon monoxide sensors, which are the most accurate carbon monoxide sensors available today. Compared with ordinary electrochemical technology, this latest technology offers higher precision, lower power consumption and longer service life. The battery smoke detector is suitable compatible indoor places such as villas, factories, shopping malls, warehouses, office buildings, etc. function -New 2 in 1 smoke and carbon monoxide detectors. High precision electrochemical sensor (the most accurate CO sensor). Infrared photoelectric sensor (the best sensor compatible detecting smoke while minimizing false alarms) -Low power consumption design: after installing 3 batteries (3 x 1.5V AA batteries, the package does not include the batteries ), you can hear the DI sound and start working normally after 2 minutes. During operation, it does not display any energy-saving design. Long standby time and low power consumption. - Loud alarm: press the test button, the smoke detector and carbon monoxide alarm are 85 dB, whether you are sleeping in the bedroom or watching TV downstairs, the sound is enough to remind you of the danger . -Easy to install: Drill two marked installation holes. Use a hammer to drive two plastic grommets into the holes. Install the bracket to the ceiling by inserting and tightening the supplied screws through the plastic eyelets.