Disconnect the BreakerDisconnect the electric breaker. Undo the screws on every sensor, and change the garage door sensors. Make certain they're only 6 inches from the ground, and fasten the strings to the sensor.
Align the Safety SensorConstrict screws on the sensors. Take off the strings, and remove modern garage doors them from http://www.garagedoorservice.com/ the sensors. Connect http://www.localgaragedoor.org/ the breaker to align the safety sensor overhead garage doors on the garage door.
References:YouTube: Safety Sensors
Garage Door Opener Guide: Garage Door Opener Installation