How effective is the water sensor?

We have our HVAC handlers in the basement, up off the floor. It seems the return conduit to get to the pump likes to get blocked up, and water leaks into the bottom then out onto the basement floor.

From the pics, it looks like the water sensor is designed to be hung on the wall. I suppose I could hang it down low on the base molding, but assume the optional water-leak cable would be the recommendation so I could coil it up and put it below the unit. (Why is it 15-feet?)

So how effective is the water sensor? I would be looking to get two, one for each handler.