Abstract: The invention relates to an improved safety device for stopping cable payout in an overspeed condition, and particularly to a safety device for securing an object from falling because of failure of a hoisting device. According to the invention, an inertial actuated drum locking mechanism comprises an inertial member mounted on a cable rewind drum. The inertial member is pivotable so that when actuated by inertial force above a predetermined value due to overspeed rotation of the drum, the inertial member moves to engage a fixed member for arresting further motion of the drum. The inertial member is held in place until the outward force exceeds the predetermined value, at which point, the inertial member toggles outward to provide rapid and positive engagement of the locking mechanism.