Weak Battery
The temperature dipped below 0 F last night and was still around 0 F when I left the house. The car started just fine, a bit to my surprise as the battery is still the original, manufactured sometime in 1996.
Another battery is a bit of a problem. The one in the remote control for the garage door opener was too cold to be effective, so I had to get out and push the button in the garage to deal with that. I had the same problem last year, and carried an extra remote control in a coat pocket so it'd stay fairly warm. I'm not sure a fresh battery would be any better than what's there now, but it might be time to find out. I think the range has been decreasing some, even when warm, but I'm not really sure of that, either.