It’s based on a SparkFun ESP32 Thing, a very compact way ... an APDS-9930 proximity sensor, as well as four CNY70 IR proximity sensors on the bottom, used for line-following.

you connect a common 433 MHz receiver module to an ESP32 or ESP8266 microcontroller, and have it wait until a specific device squawks out. From there, the code on the ESP can fire off using ...