Legacy CO Fault Indicator: Chirps every 30 seconds, Green LED off, LCD error, Power Consumption: 0.3mW, Dimensions: 10 x 3.5 cm, Power: 3 AA batteries (not included) Protect your family from Perfect item for damage by carbon monoxide, advanced protection, easy to read the carbon monoxide level detected by the device through the digital display even in low light, green LED: flashes every 30 seconds to indicate that the device is operating normally. The green LED also flashes before taking a CO reading and when any button is pressed. Red LED: When dangerous levels of carbon monoxide are detected, the red LED will flash and sound a loud alarm pattern. The carbon monoxide alarm pattern is 4 short beeps, followed by 5 seconds of silence, then 4 short beeps, and the corresponding red LED flashes. This cycle will last 4 minutes and then change to 1 cycle per minute until the device is reset or the CO is eliminated. The test/reset button is designed to test weekly if it is working properly and reset the device during CO alarms to alert the user when the battery needs to be replaced This alarm is highly recommended to be mounted on a wall surface