Near the end of White House Down the hacker, Tyler, having finished his work puts on a military uniform (probably for disguise) and tries to escape by the tunnel "through which JFK brought in the Monroe". When reaching the explosively-locked gate which Cale and Sawyer saw earlier, he tries to unlock it (with a kind of chip card, I think). Having no success he tries a second time but then says something like "Oh shit!" and the thing goes off, blowing him away.
But my question is, why were his unlocking attempts not successful? Was it really just mere bad luck that his card didn't work or was there a better reason which I might have overlooked in the story?