1. It uses an electrochemical carbon monoxide sensor-the most accurate technology 2. The permanent sensor lasts up to five years 3. The detector is easy to install and use. 4. A perfect item for protecting your family from the dangers of carbon monoxide Green LED: Flashes every 30 seconds to indicate the unit is operating properly. The green LED will also flash before CO reading is taken and when any button is pressed. Red LED : When a dangerous level of carbon monoxide is detected the red LED will pulse and a loud alarm pattern will sound. Specification: Power Supply: 3 AA size 1.5V batteries (battery not included) Sensitivity & Time: 50ppm, alarms within 60-90 minutes 100ppm, alarms within 10-40 minutes 300ppm, alarms within 3 minutes Standby Current: < 50uA (without LCD); < 200uA (with LCD) Alarm Current: < 75mA Operation Ambient Condition: 5~40,°20~90% R.H. Cautions: 1. Mounted on a wall. 2. Do not install in garages, kitchens, furnace rooms or bathrooms! 3. Install at least 15 feet away from any fuel burning appliance. 4. We suggest an alarm be installed on each level of a multilevel home 5. Needs to be tested weekly!