The Skylink MK-318-3 3-button key chain garage door remote provides a compact, pocket-sized access for up to three Skylink-brand garage doors. The remote features three individual buttons and a key chain fob for convenient carrying in your purse, pocket, or house keys. Enable the optional pass-code protection on the key chain remote and enter a pass-code before using it just like your smart-phone, to prevent break-in to your homes if your remote is lost or stolen. The password can be 2-8 digits long from a combination of button 1, 2 and 3. rolling- technology is used in communication with the receiver, changing the access after every use to prevent unwanted access. Non universal a smart button receiver is require to work model GB-318 (sold separately).A 3V lithium battery is included (model CR2032)