Keeping your ice hole clear

[Lightfoot]

Question for everyone. I had an idea a little while ago on a device to keep you ice hole free and clear of ice no matter what the temperature is outside. Needless to say a week or two later I saw my idea in a fishing magazine. My idea was some type of device that you'd put in the hole that would heat up and keep the water above freezing. My question is...has anyone else seen or heard of such a thing, and if so what's it called? Thanks for the help.
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