Where can a buy a cover for my refrigerator temperature gauge to save energy?

Question:I read about something in the UK version of 'The Week' magazine several months ago. It is a cover (I think made of wax) for your fridge thermometer. The wax stays the same temperature as the food in the fridge because it is a similar consistency, so the fridge operates more efficiently, only turning on the cold when the wax gets too warm, instead of turning on just in response to the air getting warmer (which might be completely temporary, due to door opening). I can't find it anywhere, but I know I read about it...

Thanks!

Answers:
Keep it simple poke hole in top of pop can route sensor into bottle or can works great