Every wireless access point has a MAC address — a 48 bit number that uniquely identifies it. By checking the MAC address of the wireless access point your computer is connected to, you can figure out if it is being used at home, in your office, etc.
You can read this value from the shell with the command:
arp `ipconfig getoption en1 router`
Here’s how it works. The command ipconfig getoption en1 router gets the IP address of the router for the interface en1, which is the name of the Airport interface. If you want to get the router connected to the ethernet port use en0. The output of the command looks like:
128.62.96.1
arp prints information about the IP address, including the MAC address. arp is a little tricky in that it needs to take the address as an argument, you can’t pipe the output from ipconfig into it — that’s why ipconfig getoption en1 router is surrounded in “. Output from arp 128.62.96.1 looks like:
cisco-128-62-96-1.public.utexas.edu (128.62.96.1) at 0:12:44:f:5f:0 on en1 [ethernet]
The MAC address is in there, but you may need to use a regular expression to get at it. Here is an example of a perl script which prints just the MAC address of the wireless access point, or an error message.
if (qx{arp `ipconfig getoption en1 router`} =~ /([0-9A-Fa-f]{1,2}:[0-9A-Fa-f]{1,2}:[0-9A-Fa-f]{1,2}:[0-9A-Fa-f]{1,2}:[0-9A-Fa-f]{1,2}:[0-9A-Fa-f]{1,2})/){
print "$1\n";
} else {
print "Error; wireless internet is most likely unavailable\n";
}
This is essentially how IMLocation determines location.
In summary: Using the shell commands: arp `ipconfig getoption en1 router`, and the regular expression ([0-9A-Fa-f]{1,2}:[0-9A-Fa-f]{1,2}:[0-9A-Fa-f]{1,2}:[0-9A-Fa-f]{1,2}:[0-9A-Fa-f]{1,2}:[0-9A-Fa-f]{1,2}) on it’s output, you can get the MAC-address of the wireless access point your computer is using. This gives you the computer’s location in about a 150 foot radius.
EDITED TO ADD: Another way to get this information is to use the private tool: /System/Library/PrivateFrameworks/Apple80211.framework/Resources/airport
-s gives a list of surrounding networks; -I gives information about the current network.
Try /System/Library/PrivateFrameworks/Apple80211.framework/Resources/airport --help for more information.
You can even get the MAC address of all visible base-stations this way. Unfortunately, any system update could change the Apple80211.framework enough to break your code.