This is a common burglar casing action. They buy a replacement wireless controller, program it with a base code, then drive around and see which doors open. When one opens, they drive away, then observe that family's actions to see when no one is home. They will hit that home at their leisure.
......Or else someone just happened to hit their control that just happened to have an identical code as yours, as they just happened to pass your house.
This is the best case worst scenario one. Change your code immediately.
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I don't have Alzheimer's- My wife had me tested.