If you are buying a digital thermo with probe, you might as well get one with the Min/Max feature.

If you want to know how cold it gets, at the coldest point, you can either stay up all night temping out the cage every 30 minutes, or just use the Minimum feature and see how cold it gets at 3am or 4am in the morning. Super handy.

The Acu-Rites we sell at PE have this feature, and we use it throughout the season to evaluate both Minimums and Maximums, cages, rooms, egg boxes, etc.