Shelly 1 with Temperature sensor - it's 3 wires, but all the pool water sensors I see are only 2 wires?

Hi everyone, I use a Shelly 1 to control my pool heater via relay which works great. I bought the temperature sensor add on for it which also works, but I want to install it into the PVC plumbing to show the water temperature. I was looking at proper pool temperature sensors that are designed to screw into the PVC pipe, like ones from Pentair and Hayward, but all of them only have 2 wires and not 3 like the Shelly 1 temperature sensor.

Just wondering why that is, or if I need one with 3 wires, etc. There's no way to really use the Shelly 1 temperature sensor on the PVC pipe without it leaking like crazy, so rather use a sensor designed for pool plumbing. I just have yet to find any pool temperature sensor with more than 2 wires.