The Echo Trigger allows the shooter to select from 3 different settings: Safe Mode: Firearm will not fire. Semi-Automatic Mode: Firearm fires when the trigger is pulled. Echo Mode: Firearm fires when the trigger is pulled and also when the trigger is released. The Echo Trigger is designed with safety being the utmost priority. When the shooter is in the Echo Mode and depresses the trigger one round is fired, if the target moves, the shooter can move the selector to the safe position and a second-round will not fire upon release. You will need a full auto bolt carrier in your firearm for the Echo AR-II to function. The Echo AR-II is designed to function in the AR-15 Platform. If you have any questions in regards to if you have a full-auto carrier, please visit echoquestions.com.#html-body [data-pb-style="62DF828AA2026"]{justify-content: flex-start; display: flex; flex-direction: column; background-position: left top; background-size: cover; background-repeat: no-repeat; background-attachment: scroll; border-style: none; border-width: 1px; border-radius: 0px; margin: 0px 0px 10px; padding: 10px;}#html-body [data-pb-style="62DF828AA2032"]{border-style: none; border-width: 1px; border-radius: 0px; margin: 0px; padding: 0px;}