Situations: 1. Test : Step 1: press the test botton for 5s Step 2: the unit will sound 4 beeps every 5s twice & Red LED flashes & LCD display "000" (3 min), that shows the unit in a normal situation. 2. Low Power: Sound:"Chirp" every 30s LED: Green LED flashes once every 30s & Red LED is flashes LCD Display: "Ld" 3. Malfunctioning: Sound: "Chirp" every 30s LED: Green LED is not flashes and Red LED is flashes LCD Display: "Err" 4. CO Leaked: CO level over 999ppm: Sound: 4 short alarm beeps LED: Red LED is flashes LCD Display: "999ppm" -30ppm<CO level< 999ppm Sound: 4 short alarm beeps LED: Red LED is flashes LCD Display: "actual concentration" 5. Memory Mode: If you leave home for long time, if the unit was alarm in this period, you just press the botton for several seconds, the green light will flashes once every seconds ans the LCD will diaplay the actual concentration. Note: 1. This carbon monoxide alarm is designed to detect carbon monoxide gas. It is Not designed for Smoke detect and alarm or ANY GAS detect. 2.Don't press test/reset button while installing batteries. Otherwise, the unit will not work. 3. The unit needs to be tested weekly. Verify the alarm and LED light operation by test the unit once a week. 4. The lifetime of CO detector, is depends on the sensor which build-in alarm. The lifetime of the sensor is depends on air humidit. If the alarm under a proper level of air humidit, the lifetime of alarm would be 1 year. Otherwise, it would not live more than 1 year. 5.This CO alarm uses 3 AA batteries. The lifetime of batteries would be 1 year or more than 1 year when under standby mode. The lifetime of batteries would be less than 1 year if you press the test botton often or the detector alarm often. Package List: 1 x Alarm 2 x Screws 1 x User Manual