The combination smoke and CO detector detects both smoke and carbon monoxide faster and more accurately using a photoelectric smoke sensor and an electrochemical CO sensor, protecting your home from two potentially deadly threats. Smoke and Carbon Monoxide Detector Beeping once Detecting These Two Gases. Smoke Co Alarm Detector Using High Accurate Electrochemical Sensor Alerts you to Carbon Monoxide Danger, and Photoelectric Sensor Detects Smoke While Minimizing False Alarms. Insurance Safety of your Life. 3 Pieces AA Battery - Powered Smoke Co Detector. Easy to Install. It Will Mind You Up To Change Batteries With Continuous Beeping Every 30 Seconds When The Power is Close to Run Out. The Low-Level Blink Indicator Shows it's Working. Apply for All The Place to Produce Smoke And Carbon Monoxide, Such as Kitchens, Bedrooms, Hotels, Apartment, Markets. Also Useful for BBQ Situation, Using Charcoal Warm, Garage, etc. This product has passed the UL standard report issued by the laboratory accredited by IL AC IsO 17025/NRTL standard. We have complete certificates of UL217 and UL2034 testing. Protect yourself and your family from the silent danger of carbon monoxide with our top-of-the-line Carbon Monoxide Detectors. With its advanced detection capabilities, our Carbon Monoxide Detectors ofer you an added layer of security and peace of mind. If you have any questions about our smoke and carbon monoxide detectors, please feel free to contact us. we will provide you with a lifetime free after-sales service.