Our family stayed at a hotel that offered free AT&T WiFi with an access code was distributed at the lobby.
“Just connect to the network attwifi and enter the code,” the brochure said.
The network had a captive portal, a page you had to open to enter your code before your device would be allowed to use the Internet.
Ordinarily, my Android phone (running Lollipop) detects this and shows a notification asking me to sign into the network. This time, though, it wasn’t working. On most captive portals, attempting to load any URL causes a redirect to the captive portal, but on this particular network, the HTTP requests were just failing.
After a bit of searching I unearthed two helpful bits of information:
People mentioned that their Apple devices “just work” when connecting, but have had problems with Android.
Apple devices attempt to load a well-known URL on Apple’s web site to detect a captive portal: http://www.apple.com/library/test/success.html.
The solution? I brought up Chrome on the Android phone and manually entered the Apple URL. This time the portal detected the request, redirected me to the log-in page, and all went swimmingly.
So, the moral of the story: if your Android device won’t detect captive portals, it may be that the problem is that the captive portal isn’t redirecting all URL requests–only those that seem to be sniffing for a portal. Try Apple’s URL.