Float Switch with Sonoff

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 ports S1 and S2 from the Sonoff Mini R4 to close the circuit and so I would be warned by Alexa 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.
Any suggestion? Any sonoff which I can use as a dry contact sensor?

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I use this one and it works fine.