Float Switch with smart sensor / dry contact switch sensor

Hardware
1

I bough a Float Switch that works with a floating on top of a liquid which opens or closes the electrical circuit as the liquid level rises or falls.

My idea was to use the Sonoff Mini R4 or any 1 way control smart switch to know if the state is ON (buoy is up and circuit closed) or OFF (buoy is down and circuit open), so I would know if the water level has gone down, however I’m affraid the S1 and S2 may not completly isolated and somehow I get 110V in the water tank.

I do not intent to turn on any pump, only to receive an alert on Alexa. The float swicth itself would be connected staright to the smart switch.

Any smart device I can use? Maybe a dry contact sensor? Any suggestion?

2

If you have a zigbee network you could use any door/window contact sensor (solder across the reed switch). These run off a 3V lithium coin cell and typically last several years.

Alternatively if you only have wifi then there is the Shelly Door Window 2. Runs off 2xCR123A batteries, is slightly slower to react and the batteries may not last as long.