Waeco digital fridge/ambient thermometer. The electronic display shows the temperature inside the fridge as well as the outside temperature.
You can also set an Alert Temperature so that if the temperature within the fridge gets above your pre-selected temperature the alert will beep.
A small wire with sensor is placed inside the fridge and attached with a small velcro tab. The wire extends outside the fridge to the digital display that is placed in a convenient position (out of direct sunlight).