Some simple binary indicator on a kettle that says that it's still hot from a recent boil, and switching it on would only result in immediately boiling again.

Not as complex as a thermometer or temperature readout, just a simple thing that says whether or not it's worth boiling the kettle (if it's a multi-user kettle, the previous account might have just boiled it, for all you know).
-- Ian Tindale, Oct 31 2005

Or paint, similar to this http://www.motorcyc...ory=NEWS_OTHER-NEWS
[Ling, Oct 31 2005]

You can get little liquid crystal thermometers that stick onto stuff; often used on fishtanks. I suspect they're available in a range of granularities. You would want one that only distinguishes between "> 90 degrees" (or whatever characterises "still hot") and "< 90 degrees".
-- angel, Oct 31 2005


Since most of the world is concerned with energy saving this would be a very good idea. It could be done with a floating density...um...thingy (I used to know what the were called but I have forgotten) but this may stop working over time. Electronic components are expensive if they are designed to be used at temperatures over 100C.
-- miasere, Oct 31 2005


Ian, I have also seen coloured crayons that change colour according to temperature. You could check temperature stratification if required. One could get a child to spend an entertaining half hour, legally scrawling all over it.
-- Ling, Oct 31 2005


I think a temperature indicator, even something passive such as angel suggests, is the way to go. Some drinks require boiling water, some require water that is below boiling.
-- DrCurry, Oct 31 2005


How much energy are we talking about saving here? A 2000W 10 second burst every now and then?

If the device saves you 20kJ every day, your temperature readout will pay for itself in ~35 years.
-- Texticle, Oct 31 2005



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