The invention belongs to the technical field of household appliance accessories, and relates to a gadget that can cool a smart phone after the smart phone is charged or used for a long time. The gadget mainly comprises the following parts: cotton fibers, chemical fibers or blended, a non-woven fabric outer bag, PVC with a water isolation and vapor isolation function, and/or a PP, PE thin film inner bag, Ba (OH) 2. 8H2O and NH4NO3 or NH4Cl powder (or aluminum powder and iron oxide powder), and a diaphragm having a water isolation and vapor isolation function and capable of being broken by kneading easily. The cold dog is designed into portal sachet-shaped package filled with 5-20 g contents, a user leans the gadget against the heating back surface of the mobile phone that is being used, slightly kneads the outer package bag to break the diaphragm material therein, and a strongly endothermic chemical reaction is triggered by the mutual contact of the two kinds of powder so as to absorb the heat generated by the battery when the mobile phone is charged or used for a long time.