A lock module housing containing the components of a preferred embodiment is physically mounted to the rear of a gate drive motor of an automatic gate system. A solenoid front shaft, when the solenoid is de-energized, is pushed into a sprocket attached to the drive motor, thus preventing the motor shaft from turning. To release the drive motor, the solenoid is energized. The solenoid rear shaft contacts a limit switch to indicate to the controller that the drive motor is indeed unlocked. When the controller is about to move the gate, energizing the solenoid retracts the shaft and allows normal operation of the gate control system. At the end of the gate cycle, the solenoid is de-energized and the drive motor is once again locked. In the case of a manual release, a key lock is turned from a first position to a second position to unlock the motor shaft. A mechanical linkage arm attached to the key lock pulls the solenoid shaft to its energized position, which in turn contacts the limit switch. The gate can then be back driven manually.