Alternative to IP Address Restriction

Has anyone explored other methods of restricting user logins to a few devices (besides IP address)?

I’m thinking of a solution similar to iTunes, Netflix, Microsoft Licensing. I believe they use something other than the IP address to identify a machine. That way, you don’t have to worry about whether someone has a dynamic IP address.

Mostly wondering if someone has already done this. If not, I may build my own, but my boss doesn’t want a huge custom programming bill, so I need to determine the scope of a change like this.

Thanks for your inquiry. ~ We appreciate your patience :-)

I’m not aware of any cross-browser compatible way, other than what is discussed here (MAYBE).
http://stackoverflow.com/questions/3385/mac-addresses-in-javascript

A MAC Address would seem like a logical alternative.
However, I’m not aware of any way to obtain this information reliably from within a browser.

Please let me know if you come up with something!