A white hat hacker has created a $30 device that can be used to unlock almost every car or garage door. RollJam steals the secret codes, called Rolling Code, that is generated every time you press the unlock or lock button on your wireless key, and expires once they are used. When a person presses the key fob to unlock his or her car, RollJam used its radio frequency in such a way that it first jams or blocks the signal and then covertly records it, forcing the car owner to press the button again.
Source: https://thehackernews.com/2015/08/rolljam-unlock-car-garage.html