Straight copy from OpenHaystack with small changes to flash_esp32.sh, kept here for archival purposes. Please refer to https://github.com/seemoo-lab/openhaystack for more info, all credit goes there.

esptool.py from Espressiff needs to be installed, then just simply type

$ ./flash_esp32.sh <your base64 adv key>

Additionally there are two micropython scripts in development, one for Apple's FindMy network and one for Google's. The Apple script only works with the provided MicroPython firmware (with workaround https://github.com/orgs/micropython/discussions/10080#discussioncomment-4247358 compiled in) To add your own key you need to copy the "Advertisement key" from your .keys file into the script. The Google script is still very much a work in progress, it just implemented table 8 from https://developers.google.com/nearby/fast-pair/specifications/extensions/fmdn#advertised-frames and shows up as an Eddystone with the ephemeral id as data field in nRF Connect.