At Saarland University, researchers trained a $500 telescope on a teapot near a computer monitor 5 meters away. The images are tiny but amazingly clear, professor Michael Backes told IDG.

All it took was a $500 telescope trained on a reflective object in front of the monitor. For example, a teapot yielded readable images of 12 point Word documents from a distance of 5 meters (16 feet). From 10 meters, they were able to read 18 point fonts. With a $27,500 Dobson telescope, they could get the same quality of images at 30 meters.

Here's the paper:

Abstract

We present a novel eavesdropping technique for spying at a distance on data that is displayed on an arbitrary computer screen, including the currently prevalent LCD monitors. Our technique exploits reflections of the screen’s optical emanations in various objects that one commonly finds in close proximity to the screen and uses those reflections to recover the original screen content. Such objects include eyeglasses, tea pots, spoons, plastic bottles, and even the eye of the user. We have demonstrated that this attack can be successfully mounted to spy on even small fonts using inexpensive,
off-the-shelf equipment (less than 1500 dollars) from a distance of up to 10 meters. Relying on more expensive equipment allowed us to conduct this attack from over 30 meters away, demonstrating that similar attacks are feasible from the other side of the street or from a close-by building. We additionally establish theoretical limitations of the attack; these limitations may help to estimate the risk that this attack can be successfully mounted in a given environment.