Easy to install: The CO detector comes with screws for easy installation on walls or ceilings. Requires 3 x 1.5V AA batteries (not included). No wiring required, portable and easy installation, no plug needed. Battery means constant monitoring, even in the event of a power outage! The CO detector battery can be used for about 36 months. It is convenient to replace the battery and has a long service life. High Accuracy and Reliability: Features an advanced electrochemical carbon monoxide sensor that accurately detects carbon monoxide levels in real time. Instant Alert: When the carbon monoxide detectors reach alarm levels, the CO sensor detects CO, the red LED flashes, the blue backlight of the LCD screen turns on, and an early warning is issued by a loud 85 decibel beep. Self-Test Function and Informative LCD Display: The device will beep once and the red LED flash once when powered on. "888" will appear on the LCD screen. Then, when you press the test button, the device will beep