I noodled over this in my article: http://www.wired.com/news/politics/0,1283,44444,00.html On Tue, Jun 12, 2001 at 08:58:36AM -0700, John Young wrote:
The Supreme Court's decision against thermal imaging appears to be applicable to TEMPEST emissions from electronic devices. And is it not a first against this most threatening vulnerability in the digital age? And long overdue.
Remote acquisition of electronic emissions, say from outside a home, are not currently prohibited by law as far as I know. And the language of the thermal imaging decision makes it applicable to any technology not commonly in use.
Conventional wisdom of security wizards are that the emissions are very difficult to acquire from more than a hundred yards or so, but James Bamford claims in his recent "Body of Secrets" that NSA was able to acquire leaky emissions from Russian crypto equipment 6 miles offshore Cuba in the 1960s. Advances in technology would presumbably increase that capability.