How does the military protect high-rise cities from attacks fro out nations from drones etc?

I believe that with drones and unmanned aeroplanes that attacks from countries like Iran, Pakistan, North Korea, Russia, China, Iraq, Afghanistan, Libya and many more will become more common. With countries able to make untraceable vehicles this would be an effective weapon. What is in place at some of our taller buildings like in London. Are there some type of ground to air missile defense system within the city.