There’s a huge market for 433 MHz alarm system hardware out there, from PIR motion detectors to door and window sensors ... 433 MHz receiver module to an ESP32 or ESP8266 microcontroller ...

Sadly, the captive-portal-and-login-based WiFi made the straightforward approach with a reed sensor, a magnet and an ESP32 too much of ... add-on to expose the HA API from the outside, but now ...