There is water valve in my boiler room, an I would like to know is it opened or closed. 

So I am going to use ESP8266 module to know this. The idea in general:

I will put hermetic switch on the water pipe. A magnet will be placed on the valve handle.

As soon as magnet goes over the switch, the ESP will send a notification. I will use Domoticz cloud for notifications most likely. 

If this project was interesting for you, you could buy me a cofee :)