UNIQUE DESIGN Portable and easy installation. Precise electro-optical sensor, high consistency and stability, move, or in the same place for that. Loud enough and sounds good. ALARM WARNING When a Dangerous level of Carbon Monoxide is detected, the Red LED will flashes and a loud alarm pattern will sound, Loud 85 decibel alarm with LED Flash While in the Alarm Mode for the Life-Saving Safety. SAFETY AND VISIBLE Protect the Family from Carbon Monoxide, With 3 digits LCD Displayer is Optional, Err on the LCD to indicate the unit is malfunctioning. Lb on the LCS to indicate it low battery and need to replacement. 999ppm on the LCD to indicate CO level over 999ppm. If the Co leakage is less than 999p. ENERGY-SAVING Operated by 3 x 1.5V AA Batteries (not included), The alarm sound pattern is 4 beeps every 5seconds for the first 4 minutes. In 4 minutes, it will change to 4 beeps ever minute to save the battery. ALARM STANDARD 50ppm, alert within 60 to 90 minutes; 100ppm, alert within 10 to 40 minutes; 300ppm, alert within 3 minutes. Note: When you test the detector, please do not use gas blow the hole directly.