A lot of journals transparently gatekeep their articles with a paywall, but are clever enough to grant campus IP ranges access so that they just magically work. Is there a Firefox extension that will alert you when you view a paywalled page?
It doesn't have to be 100 percent accurate or anything, just something to remind me that not everybody has access to say ACM journals.
I would be skeptical of ANY program that claims to do this. There are just too many ways to defeat such a program. Or to put it another way, there are far too many methods that a university and journals use to establish authenticity and a program would essentially have to test each one.
While you can build such a program, it's similar to the traveling salesman problem. Methods exist to solve this problem. Finding a methods that efficiently tackle such a problem have stumped the brightest minds of our generation.
A better solution is to ask for a listing of known methods to get past paywalls. But that would unethical in most circles. . .
As surfasb wrote, it's impossible to control this client-side, because IP addresses would be checked server-side. Easiest way to test would be to setup a proxy somewhere on the net, or use some of free proxies out there.
So, in theory, someone could develop an extension that would try to access the page though proxy, but I doubt anyone would give their bandwidth for free.
