Product review (5 stars): Did your frozen food thaw out and then refreeze? Find out with this cool gadget.
I bought one for my garage freezer, and one for my kitchen refrigerator/freezer. They work very well. Quite an ingenious solution, letting me know that my food has not defrosted to a dangerously low temperature.

And OK, they're a bit pricey, but the piece-of-mind is worth it. Highly recommended.