They come in a few different operating bandwidths, the 433 MHz is probably the most common ... which builds a kernel driver for the RF module. You can get your own RFM12B for a few bucks.

In essence, you connect a common 433 MHz receiver module to an ESP32 or ESP8266 microcontroller ... In the past we’ve seen the Raspberry Pi fill in as an RF to WiFi gateway for these type ...