I would like to monitor who connects to my iMac's WiFi hotspot. I have protected it with a password, but WEP is easy to crack. Is there a utility for OS 10.7.3/Lion to see who is connected?

  • Everyone should be aware of who is using his network, and that WEP is just… false security.
    – dan
    Apr 28 '12 at 18:49
  • @danielAzuelos At least in 2012, Apple didn’t offer anything better than WEP in OS X. Some systems, e.g. first Intel-powered Macs (32bit), are limited to 10.6 or lower.
    – Crissov
    Dec 13 '15 at 12:32

arp -a

gives a list of connected interfaces on the same network.

  • en1 is Wi-Fi
  • en0 is Ethernet (on the Macbook Air this is Wi-Fi)

How to use

Type this command in the Terminal located at /Applications/Utilities/Terminal.app. To learn more about this command, type man arp in the terminal.

  • In hindsight, this is a better option. Mar 17 '12 at 19:15

You could use a network map like Nmap to 'map out' your connection, and see who is connected. Alternatively, Little Snitch should let you see what they do (ie what they visit).

  • But does Little Snitch also show who's connected?
    – gentmatt
    Mar 17 '12 at 19:18
  • I've actually never tried. I wouldn't imagine so though - just the data flow in and out. Mar 17 '12 at 19:20
  • 1
    I use little snitch. When someone first connected, it gave me one prompt. After that, there is nothing showing a list of clients. Further, there are legitimate clients whose traffic I don't want to monitor. I simply want to know if additional clients are associated. I'll check out nmap too, but as you noted on the other answer, arp works well. Mar 17 '12 at 19:30

Here is a command I let in an xterm (or Terminal) running to be aware of neighbour attempting to enter my WEP unprotected Wi-Fi network:

/usr/bin/sudo tail -f /var/log/system.log | grep 'bootpd.*\[en.\]'

When this window starts to scroll, I know I got a new uninvited guest at home.

If I want to know afterward who attempted to access my network, I can find it with:

/usr/bin/sudo grep 'bootpd.*\[en.\]' /var/log/system.log
  • The Apple way would probably to keep a Console.app window open. Note that there’s Filter <kbd>⌥⌘F</kbd> and Find <kbd>⌘F</kbd> available, but no regular expressions.
    – Crissov
    Dec 13 '15 at 12:29

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