This code enables an ESP8266 device to scan/detect MAC addresses. Scanning takes place in monitor mode, which means that devices do not have to be in the same network as the ESP. You may upload this code to an ESP8266 using the Arduino IDE. With small additions, the code can be used to measure the number of active devices in the smart home or to react to your own MAC address in a certain way.
This version of the code was written for educational and private use only. In its current form, it is not suitable for professional use and I do not assume liability for any kind of functioning or legal compliance of its application.