This is kinda neat, just the other day I was reading about Weewx[1], a FOSS project to allow "roll-your-own" weather stations.
My in-laws have a pretty fancy weather station in their backyard, but its tied to a proprietary LCD weather screen in their living room. I've admired it for a while but daydreamed about building my own more flexible system when I get a house.
Those fancy weather stations often transmit to the indoor LCD display using fairly simply messages sent in the 433 MHz band or the 915 MHz band. For many those message formats have been reverse engineered and decoders for them added to open source SDR software such as rtl_433 [1].
With a $30 USB RTL-SDR and rtl_433 you can then use the sensor units from many of those fancy units as inputs to your own display and analysis software. And you can often use your neighbors' sensors too. One of my neighbors--I still haven't figured out which--has an AcuRite 5-in-1 system and I can see its readings using my RTL-SDR and rtl_433.
If you build your own sensors it is cheap and easy to add a 433 MHz transmitter and define your own message format. Rtl_433 can be extended to cover new message formats by giving it a config file that describes the formats.
There's a driver for Weewx to let it use rtl_433 [3].
You can get an RTL-SDR and rtl_433 now, and start playing around with whatever sensors others in your neighborhood happen to have.
[1] https://github.com/merbanan/rtl_433
[2] https://www.acurite.com/shop-all/weather-instruments/weather...