Yesterday, my wife came home (in the Roadster) and said she noticed the Model S hatch was open as she drove in. And I just went out in the garage, and noticed the hatch was open again.
A week or two later, the weirdness continued. The hatch opened two more times, the windows rolled down twice, and the car unlocked itself once - all within the space of a few days. And always in the garage.
I noticed that all of these are things that you can control from the key fobs, which we store not far away. I did verify that while the fobs were far enough away that the car stayed locked even if I pressed on the door handles, the fobs were close enough that if I pressed a fob button, the car would obey. But why would the fobs send random messages? We tried moving the fobs far away for a couple of weeks, and sure enough none of this happened.
But while we were still storing the fobs away from the car, we started getting "key fob battery low" error messages when we drove the car. So I replaced both fob batteries, and stored the fobs back near the car.
The good news:
1. The problem has not happened since
2. If this really was the problem, it was only a risk in the garage. (It wouldn't have opened the hatch at a grocery store, because the fob would be too far away)
3. Tesla replaces fob batteries at the yearly service, and generally the batteries should live much longer than that (see next item), so most people shouldn't see this
Questions I still have:
1. Why did the fob battery die after only 4 months? Tesla says early cars (ours is VIN 112) had the fobs stored inside for transport, which apparently uses a lot of fob battery. They now transport the fobs separately.
2. Why would a dying fob battery send random signals? You'd think if the battery was weak, it would just sit there quietly.
3. How can I be
sure I have fixed the problem? It took months to show up at all, and then didn't happen for a couple of weeks at a time. I'd feel better if I knew the answer to #2, but all in all I think this was very likely the issue.