The MegaCode ACT21 is a compact 1-button keychain remote designed for garage door and gate openers using the Linear Moore-o-Matic Megacode system. Operating at 318 MHz, it features a smart coding system without dip switches for secure and straightforward use. Measuring just 2" by 1", this transmitter includes a key ring and offers battery life lasting up to five years under normal conditions. It is fully compatible with all Linear Megacode system devices.