Built-In 10-Year Battery: Built-in 10-year lithium battery spares you the hassle of frequent battery changes; Provides uninterrupted 24/7 protection..2-in-1 Protection: Equipped with an electro-optical smoke sensor and an electrochemical CO sensor to protect your home from 2 potentially deadly threats..High Sensitivity & Accuracy: Upgraded photoelectric and electrochemical sensors significantly improve alarm sensitivity, thus speeding up response time while minimizing false alarms..Automatic Self-Check: The smoke and CO detector automatically checks battery level and sensors every 60 seconds to ensure they are working properly..Ultra-Thin Design & Large Button: This device measures only 1.1 in thickness. Portable design also suits for travel. Test or mute your alarm by simply pressing the button using a long stick rather than a ladder..Quick Installation: Easy to install this smoke detector carbon monoxide detector combo with the provided adhesive tape or screws, without the need to hire an electrician..90 Days Full Refund or Replacement: Not satisfied with our product? Return it to us within 90 days and get 100% of your money back! We also provide a 5-year warranty..Activate Before Using: Press and hold the test/silence button for 10 seconds until the led indicator lights up, then release the button. The alarm will generate a beep to indicate activation succeed.