The Echo AR-II Trigger is an ATF approved trigger that allows for fast follow up shots for great fun at the range. The Echo AR-II 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 AR-II 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. PATENTED Mfg: Fostech Outdoors, Llc.