When a dangerous level of carbon monoxide is detected the red LED will pulse and a loud alarm pattern will sound. Standby: Green Led flashes once every 30 seconds. Alarm: Red Led quickly flashes 4 times with unit chirping every 5 seconds， then repeat. Sensitivity/Alarm Time: <20ppm，LCD displays 0ppm. 50ppm， alarms within 60~90 minutes. 100ppm， alarm within 10~40 minutes. 300ppm， alarms within 3 minutes. A test / reset button allows you to test that alarm is functioning properly. Plus a peak-level memory keeps track of the maximum CO level detected between resets. The CO detector is a battery-operated independent carbon monoxide (CO) alarm and with the inside carbon monoxide sensor to help protect you and your family from the dangers of CO.The detector is easy to install and use .In a CO emergency， the red LED pulses and an 85 db horn sounds at specific intervals until the CO threat is eliminated.Technical parameters:Power supply: 3 pcs 1.5V 5# batteries (not included) Monitor current: less than 35 uAAlarm current: 20mA or soAlarm concentration: 50 (± 30%) ppm of carbon monoxide gasLow-voltage warning threshold voltage: 3V ± 0.3 VEnvironment: Temperature: 0 ° C ~~ 45 ° C， relative humidity: 20% ~ 95% non-condensingAlarm sound: three meters in front of more than 85 db;