> These devices are designed to work for hours with minimal supervision.

I wish. A while back, I put some (food) stuff to dry in the oven on a very low heat, knowing it would take all night to dry fully. After six hours, the oven decided that I must have accidentally left it on by mistake, and switched off automatically, and that stuff was wrecked when I got up in the morning and checked on it.

Indeed. I don't think I've ever heard of an oven burning down a house. And given how pretty much everyone has one, there must be many ovens left on alone in the house at every given moment.