Homekit, temperature with DS18B20

Updated 2021-04-15 !

A cheap and simple way to measure temperature, and have it displayed in the Home app, is to connect one wire (1W) DS18B20 (DS)temperature sensors direct to the Raspberry Pi(RPi) and install a DS plugin.

This assumes that You have Homebridge up and running on a Raspberry Pi 

Check this post !!  "ANY" temp source can be HomeKit enabled.