One of the oldest objects in my possession is a twenty-odd year old bed warmer I will always think of as my sister's because mine was of different construction, although really both belong to the InnerRents.
It is, I feel, a masterpiec of simplistic design: merely a light fitting inside a mesh cage inside a much bigger solid wire cage, altogether about 60x30x20cm, and certainly enough to create a section of air when the duvet is placed over the cage, so that when plugged in, the heat generated by the lightbulb heats up the bed. I've never met anyone who has one, and yet it's genius in its simplicity.
Except when the only lightbulbs one has in the house are of the energy-saving variety. Those don't give out much heat. Or any at all, actually. Just when I need it, bugger.
Still, getting a new boiler this week. Probably.