Abstract: A device simply and effectively senses undesirably high temperatures in a refrigerated volume with an accuracy of about 3 percent, and activates an indicator in response to the sensing. A temperature probe is disposed in a freezer, refrigerator, or cooler volume, the probe including a negative temperature coefficient thermistor forming part of a voltage measurement bridge. The resistors of the voltage measurement bridge are all accurate to one percent, and are connected up to a voltage comparator of an integrated circuit. A 9 volt battery powers the device. The device also includes a low battery voltage sensor for activating the indicator when the battery voltage drops below about 8.2 volts, and a sensor for detecting when the probe is damaged or disconnected. The probe detection circuit includes a Darlington transistor, and resistor, the Darlington transistor being connected through a diode to the indicator. The indicator may include a piezo electric horn driven by a horn oscillator circuit.