Check out AcuRite's Digital Refrigerator and Freezer Thermometer. You can usually get it cheaper on Amazon, or wait for a sale on AcuRite.com
https://www.acurite.com/digital-freezer-refrigerator-thermometer-with-temperature-alarms-00986.html
https://www.acurite.com/digital-freezer-refrigerator-thermometer-with-temperature-alarms-00986.html