Ah right from way you were talking I thought it was one with a high and low temp setting. One of mine has this and it's set between 29-33 and it's set to alarm if it goes +/- 2 degrees either way. Pretty handy but can be a pain to get working. I only got it as I was buying a snake from someone and they offered me it for £10.
1.0 Milksnake 3.3 Kingsnakes 1.1 Royal Python 1.2 Cornsnakes