The Fostech Echo Trigger allows the shooter to select from 3 different settings: Safe Mode: Firearm will not fire. Semi-Automatic Mode: Firearm fires when trigger is pulled. Echo Mode: Firearm fires when trigger is pulled and also when 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.The echo trigger has several distinct features: PATENTED Design that gained ATF Approval (Patent # US 8820211 B1) PATENTED Technology licensed through Franklin Armory inside the Echo AR-II Trigger including U.S. Pat. Nos. 9952012 and 9952013. Technology licensed through HIPERFIRE inside the Echo Trigger Light clean and crisp pull in Semi-Automatic Mode The Echo Trigger is packed full of cutting edge technology Reliable function in Echo Mode