Just bought my first home which has two bathrooms. We have guests stay over fairly often (family, friends etc) and on more than one occasion someone's shower has been ruined because either someone downstairs runs the hot tap (washing dishes etc) or someone else switches on the other shower, which makes both run cold.

Is there some cheap way of rigging up a switch (RF, I guess) which someone could press when about to get into the shower, which would light up a corresponding switch/light in the other bathroom (and/or in the kitchen to warn us not to run the taps)?

Or indeed, any better solutions to this problem (other than asking our guests to tell us/each other when they're using the water, which hasn't worked so far...)?

  • What size water heater? Have you seen this: diy.stackexchange.com/questions/24627/…
    – mikeazo
    Feb 26, 2018 at 14:42
  • I’d spend money fixing the real issue, not buying a band-aid. Have you ever actually seen such an indicator system being used? That’s because you shouldn’t need one....
    – Tyson
    Feb 26, 2018 at 16:00
  • Perhaps low volume shower heads. They provide good showers but use less water.
    – Yehuda_NYC
    Feb 26, 2018 at 16:03
  • how much spare electrical service do you have? Feb 26, 2018 at 16:26

1 Answer 1


This is the sort of thing that's trivial with new tech, and quite involved (expensive) without it.

It's easy with a few smart things. Assuming hot showers, a humidity sensor can trigger action. powering a dummy sensor with the exhaust fan circuit could trigger. or use a microphone sensor, or a PIR (motion detector) above the shower. Once the trigger's in the system, you can have any output you want, like a smart outlet or app notification. You can even setup "gates" around it like min/max trigger duration, debounce, etc, that would be god-awful to do in "analog".

The system can be a home-rolled node-red setup, or a commercial turn-key like SmartThings or HomeKit. The initial setup would be cheaper than fixing the problem, and then you could do lots of other neat things. If you don't have one already, it's the way to go, and if you do, then just add a new sensor and call it a day.

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