A decock/safety allows the hammer to be dropped on a live cartidge without discharging, via disengaging, retracting or covering the firing pin. So long as the safety is in Decock position, the hammer may not be cocked and the trigger is disengaged. This differs from a decock only, in that a decock only gun will allow the hammer to be cocked or the trigger pulled in DA mode once the decock lever is released.