If you need to open the gate when the power is out, you can easily do so manually with the small key on the keychain. The box with gate motor is on the left on the inside of the gate.
Insert the key and turn it counter-clockwise. Pull on the plastic door. That disengages the motor gear from the gate and you can move it freely at this point. Make sure when moving the gate to do it away from the concrete posts to make sure you don't squish your fingers. Ouch!
Once you've moved the car through the gate, simply push the gate closed, close the door for the motor, and remove the key.