Constant differential freezer thermostat with an auxiliary alarm switch circuit to warn of rising freezer compartment temperature. The contacts of a 3ART7 close on a temperature rise. The capillary sensor is normally attached to the evaporator. Variations in temperature of the capillary cause the snap action switch to make or break the electrical circuit to the compressor. An integral auxiliary switching mechanism is added which closes the contacts to a warning lamp or buzzer circuit when the temperature in the freezer compartment reaches a specific number of degrees above the compressor "on" temperature.