Only limit on what works is the range of the thermometer. Many meat thermometers don't register less than 100 degrees so that is no help.

Any cheap vertical tube outdoor thermometer - skinny tube of glass or plastic filled with a red liquid (used to be mercury) - works. Available at Walmart for a couple of dollars.

Dave

Here is a link that might be useful: Example of thermometer

Thanks Dave mine actually registers under 100, it's says 79 in my kitchen now which is about correct. So I guess it should work in soil then.

I use the kind with the probe that goes into the meat, or the soil. No wire. It goes down to the freezing point.

I check the soil temp in the spring for first planting and again in the fall.

btw, I understand that 4 inches down is the right depth.

There are simple kitchen thermometers that has a range of 0F to 220F. There are both with digital and analog displays. I have the latter. It has a probe of about 6" long.
You can find one in the household/kitchen ware section in most supermarkets.