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This is just for crt, or lcd too? Just curious.

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It's tough to find a definitive answer - for obvious reasons this stuff isn't published that much on the web. CRTs emit radiation that can be detected and isolated up to a 1/2 a mile away. With the right equipment you can easily view the screen image on a neighbor's CRT in real time, and it's not that expensive. There have been serious issues with bank security resulting from this capability.

Any electromagnetic device emits radiation when it is operated, and from what I've read the radiation from LCDs is easily detected and reconstructed, but it's of significantly less strength than CRTs. My guess is the effective range is probably 50 or so metres (the similar effective range for devices like microchips and RAM), but it's hard to be sure.