Are you telling me the x-ray machines I go through each day just detect the glass bottle that would contain the beer, and not the beer itself? Geez, this could be a revolutionary revealation.
bring stout, preferably from Founders (smaller, round bottles). remove label (can be soaked off, OxyClean or other detergent will help). use magic marker to black out some or all of the cap. pack inside a bag with your lunch. when asked, claim that it's root beer. profit.
One time I DID bring root beer with my lunch and the xray machine caught it (the glass bottle, I assume?). I tried explaining the difference between root beer and beer to the guard but he wasn't buying it. Apparently, they hadn't explained the difference to him in his African country of origin. Thankfully, his more Americanized colleague was observing what was happening and stepped in to explain that root beer was nonalcoholic.
True story.