Why is My Garage Door Opening by Itself?
Q: How to stop what garage-door manufacturers call "phantom operation"
One morning after a thunderstorm, I noticed that our garage door was open. I know I'd closed it the night before. Now the door periodically opens all by itself. What can I do to prevent this from happening? —Aberdeen Lepley, Selinsgrove, PA
I talked to some garage-door manufacturers about this problem, which they call "phantom operation," and they tell me that a power surge can damage the electronics inside the transmitter. So maybe lightning really did open your door. But there could be other causes, as well.
If you live near a military base, openers can be triggered by equipment operating on the same frequency. Also, it's fairly common for a remote opener to be accidentally activated when left in a kitchen "junk drawer." The chances are low that a neighbor with a similar opener could operate yours. I'm told that older transmitters, with their nine manual "dip" switches, have more than 14,000 possible code combinations for each opener. The "rolling code" security on newer doors makes it virtually impossible for a remote to activate any opener it doesn't belong to. They can have 100 million or more combinations.
Unfortunately, if lightning did scramble your opener, you'll have to get someone in to service or replace it. Your best bet would be to call a company that installs the brand of opener you have.
— This Old House host Kevin O'Connor