Occasionally one of us in our house leaves the hot tap/faucet running, and sometimes this can be overnight, which is costly.
Any good ideas on how to prevent this?
So far I've thought of these:
Set up some kind of electronic alarm which detects heat or running water and sounds after a few minutes. But this could be quite hard for me to set up, and would probably use batteries all the time - more cost and work to monitor and change occasionally.
Set up some kind of simple alarm which detects heat or running water without much electronics (e.g. a rubber band on the hot water pipe, or the waste pipe, which should tighten as it heats up, thus triggering a switch which completes a circuit and sounds an alarm). I like this kind of idea, but my tests so far show no noticable change in length of a rubber band after running the hot tap for a while, when wrapped around these pipes, so I'm not sure I can get this to work. An alternative could be to use metal which bends in one direction when heated (I think this has 2 strips of different types of metal which expand at different rates with heat, glued together size-by-side).
Install some kind of whistle on the taps, so they make a noise when they run. But aside from the irritating noise (especially at night), I doubt these would work with very slow water flows (e.g. which could even be a fast drip).
Prevent people from using the hot tap (e.g. duct tape the hot tap handle). Not very user-friendly, and then they'll probably leave the cold tap running, which is also not ideal.