And it was Mythbusted
Rocky: That trick never works!
DrDeth & LSLGuy probably have it right – they forgot to actually lock their car, but thought they had. Then when they were returning to the car, they hit the fob button, which actually locked the car. So they found it locked, which confirmed their expectation that they had locked it when leaving. Local police have mentioned that this is a pretty common scenario.
Some newer electronic systems have a mode where the car automatically locks when the driver leaves (the key fob gets out of range of the car).
I have never seen a fob where the same button both locks and unlocks the car.
Back when I had fob you had to push buttons on, I’d hit the unlock button as I was still 10-15 feet away from the car walking towards it. Whether the car had been locked or unlocked a moment before, I got the same response: the car beeped and the doors were unlocked.
That is actually a good thing. Their only purpose seems to be as a nuisance. (I had an idea for a car alarm that would be tied to an app on the owner’s cell phone, and would only make noise or alert there. That way the only person annoyed by the noise is the person who owns the car.)
Mine does that. But it’s an aftermarket one, not a manufacturer fob. And for a 22-year-old vehicle.