Food warning device containing a rechargeable phase change material

A heating device for food and other products is provided. The device includes a unit containing a rechargeable phase change material which is capable of being charged with heat energy by a heat source such as a conduction, convection, radiant heat, electrical resistance, electrical inductance, microwave, or radio frequency. The phase change material may be provided in a variety of forms and may comprise linear alkyl crystalline alkyl hydrocarbons, alkyl hydrocarbon waxes, crystalline fatty acids, linear crystalline primary alcohols, ethylene copolymers, polyethylene, polyethylene glycol, polyethylene oxide, and acetamide.