[EN Certification] With carbon monoxide detectors, you will feel comfortable, safe and confident. [Ultra-high Sound Alarm] The carbon monoxide alarm will detect carbon monoxide levels 24 hours a day. The alarm duration depends on the carbon monoxide level. 50-100PPM, alarm after about 80 minutes, the red LED flashes every 2 minutes; 100-300PPM, alarm after about 30 minutes, the red LED flashes every 2 minutes and beeps; >300PPM, alarm after about 50s, the red LED flashes quickly and a continuous beep >86dB. [Digital LCD Display] The LCD screen displays the CO concentration level in PPM, temperature, humidity and battery status. And three LED indicators show three working states: Red (alarm mode: red LED flashes quickly, buzzer emits a "beep beep beep" sound), Yellow (fault mode: yellow LED flashes twice in about 60 seconds, accompanied by two "beep beep" buzzer sounds), Green (power on, normal standby mode). [Replaceable Battery Carbon Monoxide Alarm] 3x1.5V AA (batteries included)