I balked at the price of a good compost thermometer but have always been curious as to how hot my pile was getting. So, I got to thinking. Which often gets me in trouble. But this time, I think I may have hit on a decent idea.
I bought an inexpensive wireless indoor/outdoor thermometer from Amazon,
and I put the outside sensor into a number of used ziplock bags. 
Then I just put it into the pile under the most recent addition.
Which in the interest of good taste shall remain unidentified.
It works as well as I had hoped. It got over 130 Fahrenheit after this addition.
I don’t even have to go outside to check!
The only downside that I can think of is that I can’t get readings from different areas of the pile. But just knowing that it’s cooking is the main thing. Plus changing the batteries might be a bit of a pain. But I haven’t had to do that yet.