My wife has a small train set she puts around the Xmas tree. It's nominally G scale but definitely in the toy category. Huffs and puffs and whistles from a remote control.
Twice so far this year it's decided to go for a run on its own. Once in the middle of the night :-).
This morning I looked at the remote control. It's not line-of-sight infrared, it's radio! Someone nearby has a car alarm or garage door control running at the same frequency :-).
I guess we'll take the batteries out when not running it :-).