I cobbled together one with a PEX valve and microswitch. The microswitch finally broke. Tornado's looks more robust than mine was. I have some magnetic prox switches I was going to try with a relay, but never got around to it. Seems to me IJ used to sell his for about $120 so the price has gone up.
There's some interesting stuff on tonight, like the LED headlamp and the petcock lube as well as this one.