Is there a way to detect 802.11 devices "pass by" an wifi hotspot.

Like if an mobile user there do not connect to the wifi, But has walking by the wifi hotspot.


Mobile devices will transmit probe requests, looking for known networks. These can be detected by using a sniffer. But you need to check multiple channels since you don't know which one the user is transmitting on. Some enterprise-grade access points can scan channels looking for transmitting radios.

  • To add to Ron's answer - probe requests can be detected without enterprise-grade equipment. There is some interesting research being done about just how much information can be gathered and tracked from these requests. For example: If you detect a device with a similar probe request at a certain time each day, you can "fingerprint" this device and start to track their movements. This talk gives a great overview (warning, adult content) youtube.com/watch?v=WVPe_EPiczk.
    – alcafly
    Jun 13 '18 at 10:59

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