Have you considered that someone could be reading what's on your monitor from a few rooms away? It's unlikely, but possible, as work by Cambridge University computer security researcher Markus Kuhn shows.
A radio antenna and radio receiver - equipment totalling less than £1000 - is all you need.
Back in 1985, Wim Van Eck proved it was possible to tune into the radio emissions produced by electromagentic coils in a CRT display and then reconstruct the image. The practice became known as Van Eck Phreaking, and NATO spent a fortune making its systems invulnerable to it.
If everything is just right, you can pick up signals from some distance. "I was able to eavesdrop certain laptops through three walls," says Kuhn. "At the CEBIT conference, in 2006, I was able to see the Powerpoint presentation from a stand 25 metres away."