There are a few reasons this could be happening. If other users on the network aren’t making heavy use of the connection, then there won’t be much data for you to detect. If your phone has a connection to the network, try streaming a video or something while the script is running. Another problem could be that the script doesn’t have the right permissions to run on your system, in which case you will notice that the progress bar doesn’t get to the end. As a quick test, try increasing the number of packets to capture with
-p 10000, do something with your phone or another wirelessly connected device, and check the results again. As a final comparison, an app that has very similar behavior to this script is Debookee (Mac only) which you can use in “Wifi Monitoring” mode for even more data (and in realtime!). If you have more difficulties I recommend posting an issue to the GitHub repository rather than posting a comment, since Medium makes it difficult to follow all the comments.