Electric over blanket is used by covering human body to keep warm.
Normally electric over blanket is not recommended to be used during sleeping, as it might cause overheating, although it has the function of overheating protection.
Normally over blanket shuts off after 2 hours, for the sake of safety.
Below image as reference:
Electric Over Blanket
Electric Over Blankets, Heating Cover Blanket, Heated Over Blanket, Electric Warming Blanket
Ningbo Makeheat Electrical Appliance Co., Ltd , http://www.makeheat.net