Tools

howmanypeoplearearound – Count the number of people around you by monitoring wifi signals

howmanypeoplearearound

howmanypeoplearearound – Count the number of people around you by monitoring wifi signals

howmanypeoplearearound calculates the number of people in the vicinity using the approximate number of smartphones as a proxy (since ~70% of people have smartphones nowadays). A cellphone is determined to be in proximity to the computer based on sniffing WiFi probe requests. Possible uses of howmanypeoplearearound include: monitoring foot traffic in an area with Raspberry Pis, seeing if your roommates are home, calculate how many people are on the bus, etc.

Tested on Linux (Raspbian and Ubuntu) and macOS.

Getting started

Dependencies

WiFi adapter with monitor mode

There are a number of possible USB WiFi adapters that support monitor mode. Personally I prefer the TN722N which is only ~$10 and works great with every model of the Raspberry Pi. Here is a good list of adapters that support ‘ad-hoc’ mode for the Raspberry Pi.

tshark

sudo apt-get install tshark

Then update it so it can be run as non-root:

sudo dpkg-reconfigure wireshark-common     (select YES)
sudo usermod -a -G wireshark $USER

You will need to logout and log back in for changes to effect.

Install

If you have Python installed, run this command

pip install howmanypeoplearearound

Run

First determine which adapter you want to use to scan (usually its wlan1), which you can find the name of using ifconfig. Then, to run, just type in

$ howmanypeoplearearound
Specify WiFi adapter (use ifconfig to determine): wlan1
Using wlan1 adapter and scanning for 60 seconds...
[==================================================] 100%        0s left
There are about 3 people around.

You can modify the scan time, designate the adapter, or modify the output using some command-line options.

$ howmanypeoplearearound --help

Options:
  -a, --adapter TEXT   adapter to use
  -s, --scantime TEXT  time in seconds to scan
  -o, --out TEXT       output cellphone data to file
  -v, --verbose        verbose mode
  --number             just print the number
  -j, --jsonprint      print JSON of cellphone data
  -n, --nearby         only quantify signals that are nearby (rssi > -70)
  --help               Show this message and exit.

You can also generate an JSON-formatted output to see what kind of phones are around:

$ howmanypeoplearearound -o test.json -a wlan1
[==================================================] 100%         0s left
There are about 4 people around.
$ cat test.json
[
  {
    "rssi": -86.0,
    "mac": "90:e7:c4:xx:xx:xx",
    "company": "HTC Corporation"
  },
  {
    "rssi": -84.0,
    "mac": "80:e6:50:xx:xx:xx",
    "company": "Apple, Inc."
  },
  {
    "rssi": -49.0,
    "mac": "ac:37:43:xx:xx:xx",
    "company": "HTC Corporation"
  }
]

A higher rssi means closer (one of these phones is mine, and the other two are my roommates’ who were upstairs).

You can create a log file with the number of people this one-liner (make sure to change your adapter):

$  while :; do echo "`date` `howmanypeoplearearound --number -a wlan1 -s 180`" >> log; sleep 1; done

How does it work?

howmanypeoplearearound counts up the number of probe requests coming from cellphones in a given amount of time. The probe requests can be “sniffed” from a monitor-mode enabled WiFi adapter using tshark. An acccurate count does depend on everyone having cellphone and also scanning long enough (1 – 10 minutes) to capture the packet when a phone pings the WiFi network (which happens every 1 to 10 minutes unless the phone is off or WiFi is disabled).

This is a simplification of another program I wrote, find-lf which uses a similar idea with a cluster of Raspberry Pis to geolocate positions of cellphones within the vicinity.

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