I have three temperature/humidity sensors: one under the deck, one in the greenhouse and one in the garage.
They are RF transmitters operating at 433 MHz and I found that you can decode their info with a DVB-T USB stick ($20) and the rtl_433 command-line tool (https://github.com/merbanan/rtl_433), and feed it to #HomeAssistant via #MQTT.
This is pretty cool.
Instance perso. Principalement en français. Personal instance, mainly in French. Linux, OSS, Santé Mentale, 3615 MaVie.