I made a python script that monitors the devices around you and alters you if a new non-beacon shows up. Allowing you to detect if someone carrying a wifi-enabled cell phone is nearby. Most of the explanation for this one can be found in the README on the Github page, so for the real details.
Tl;DR I made the 'ping' quickhack from cyberpunk but it's soykafy.
Here Have A Picture: