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All, I'm working on a project at the moment where I need to count the number of unique cell phones in a room using a raspberry pi. The easiest way I've come up with to do this would be to passively scan for wireless clients.

If I use something like airmon-ng is it possible to detected devices who have wifi enabled but is not connected to any AP?

Is there a better way to count the number of distinct mobile phones in a room?

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Some mobile devices deactivate Wi-Fi when in standby, iOS was always notorious for this. So bluetooth may be a better option.

But if you do want to scan for Wi-Fi connected clients, it is much easier if you are all on the same network (e.g. the Pi and the phones connected to the same AP). Then you can simply run an arp scan

sudo arp-scan --localnet --macfile=/home/pi/mac-vendor.txt

In this example, I've also given a vendor file which lets arp-scan return meaningful names for known devices.

Otherwise, you should look at some Bluetooth utilities that will let you scan in a similar way though I warn you that the intricacies of Bluetooth make it fairly horrible to work with in my experience.

A tool such as Node-RED may be helpful to let you do the scanning and reporting without loads of programming. The Node-RED forum has plenty of people who regularly do this kind of thing for fun.

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  • Thanks! If I were to use the arp-scan method at a tradeshow where the network setup is out of my control is there anything that might hinder me trying to use this method? – user316114 May 22 '17 at 20:20
  • Haha! Yup, apart from being arrested in some countries you mean! There is no reliable way to do what you want if you can't control Wi-Fi and/or Bluetooth. Many phones won't turn on BT or won't connect to Wi-Fi and so will be missed. The only way would be to use a false cell tower to override access and then you WILL be arrested! – Julian Knight May 22 '17 at 20:26
  • Haha, I have permission from the hotel. But I don't want to make them change anything for me either – user316114 May 22 '17 at 20:27
  • I think you should update your question and restate the actual problem you are trying to solve. For example, explain WHY you want to do this and what the outcome should be. It may be enough to count Wi-Fi connections and that could be done directly from the AP. – Julian Knight May 22 '17 at 20:29

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