Having the Water Watcher display in the master bathroom does at least solve part of the problem. Decoupling the Water Bug from any listeners via MQTT messages means that I can change the Water Watcher and add any additional listeners without necessarily having to update the Water Bug or the existing listeners.

Here is the original Water Watcher patiently standing by in the master bathroom. Oh, look, the pilot light is working correctly.

There is another bathroom with a shower where I might put another clone of the Water Watcher. It's trivial to do with another M5 Atom Matrix. M5 makes a couple of other variations on the M5 Atom.:

• The M5 Atom Lite is a couple dollars cheaper. It has only a single RGB LED instead of a matrix. 
• The M5 Atom Echo, still about US$10, also has a single RGB LED, but it contains a microphone and speaker. That gives the possibility of some kind of audible alert. (Now, if I could just work out a way to give a voice command to re-light the pilot light from the cozy comfort of my warm bed. Hmmm.)

There are lots of available MQTT clients for Android phones, so I can consider getting some kind of PagerDuty-like wake-up when the pilot light goes out. Although I'm not that crazy about getting up at 3am to reboot the server, uh, I mean to re-light the pilot light, it's all-in-all better than discovering that it's needed at exactly the time when the hot water is needed.

I guess I could train the family cat to re-light the pilot, but he's not allowed to go down into the basement. I could train him to recognize the "pilot_off" display and wake us up, but it would be hard to distinguish that from the other conditions where he wakes us up in the middle of the night ("Timmy fell down the well!", "are you still alive?", "I'm hungry/thirsty/lonely").

OTOH, this cat looks pretty obedient: Meow — the Slack Bot with the smart paw