Nevertheless, spy satellites remain a valuable source of intelligence. Even commercial satellites have an image resolution of one metre - easily good enough to track the movement of tanks and most military hardware. Radar imaging can pierce cloud cover and even expose subterranean development - useful if you suspect the enemy of stockpiling arms underground. One reason is that without them spies would be able to eavesdrop on top-secret conversations almost effortlessly. Laser microphones can pick-up conversations from up to a kilometre away by monitoring window vibrations.
Curtains are a simple antidote, since they help absorb the sound and so corrupt any signal.
Despite the fact computer technology has led to quantum leaps in intelligence gathering, low-tech still has its place. One was to find a sympathetic source inside the White House who could feed you information. The other was to take out a subscription to the New York Times.