Sniffer to log telegrams on KNX Bus You need a ESP32 and a little bit of Hardware. Connect them as showed in the following schematic.
from https://www.freebus.org/content/freebus-grundschaltung
Bustiming: https://freebus.org/system/files/01_bits_und_bytes.pdf
Description of protocol: http://www.see-solutions.de/sonstiges/KNX%20Twisted%20Pair%20Protokollbeschreibung.pdf