If you've ever shivered under chilly sheets, this is a device you can appreciate.
To warm the bed at night, you placed hot ashes and coals into a closed copper skillet with a long handle, and you ran the hot pan over the sheets before sliding into bed. In wealthy families, this job might have been handled by a servant.
Families who couldn't afford a specific appliance for the task might have warmed a brick in the fire and placed it at their feet or held a hot water bottle. Unlike the modern electric blanket and mattress pads, these items lost their steam before morning. But they didn't come with stubborn cords to straighten out.
These wireless, portable warming devices have become coveted museum pieces.