Interesting idea; thanks for the link. Like you said, I’m worried about the lag after the water has been turned off, but it could be a fun project to try.
I have one of these connected to a contact sensor monitoring the supply line of my water-to-air heat pump. Works fine.
I’m intrigued, but …what am I looking at? 
An inline flow switch. When there is a flow in the pipe the paddle moves and closes the contacts. Connect a contact sensor with leads like the EcoLink DWZWAVE2.5-ECO. (I'd install it in a horizontal section of pipe.)
This may be more plumbing than it is worth for a shower, depending on accessibility, but it is the does the trick simply & quickly detecting fluid flow on HE.
1 Like
I would say this is a device issue or limitation. I have tested a few devices, and some are noticeably slower than others, some to a point where they are as you note, worthless for this.
Maybe list what device(s) you have tried?
This is a recent relevant thread that might be useful.
1 Like
I have the Konke sensors. They send an update every 30 minutes or when there is a humidity change of at least 5%. I’m actually not sure if those are configurable, although I don’t see anything obvious in the driver. They work great, and I’ve used them to automate the exhaust fans with great success. But in order to get the first 5% change, it definitely takes longer than a minute from when the shower turns on or off.
I am not very familiar with these, but which driver are you using?
I think @JasonJoel and @aaiyar use these (or did?) so maybe they can comment on these sensors performance and how configurable they are.
I’ve been using this one:
Ask and you shall receive 
1 Like
I would add unplugging Alexa to my shower routine 
5 Likes
Wow, now that’s a cool idea! I’m not good enough with electronics to know what to do with this, but it might motivate me to learn. Downside is that it still may not be enough for my use case:
The only thing left is AI and a camera 
1 Like
