The only one battery powered temperature sensors with external probe I know are from Ecowitt:
A Homey App is of course available (Misol and Ecowitt), but I recommend to check in the related topic, which of them are supported.
In addition, you should find out which of these sensors is really suitable for this application (IP protection class, resistance to chemicals, e.g. chlorine).
And please note the transmission frequency. Depending on the region, only a certain frequency is permitted.
