On the Effectiveness of Aluminium Foil Helmets: An Empirical Study
Electrical Engineering and Computer Science department, MIT.
"It has long been suspected that the government has been using satellites to read and control the minds of certain citizens. The use of aluminum helmets has been a common guerrilla tactic against the government's invasive tactics [1]. Surprisingly, these helmets can in fact help the government spy on citizens by amplifying certain key frequency ranges reserved for government use. In addition, none of the three helmets we analyzed provided significant attenuation to most frequency bands."
http://people.csail.mit.edu/rahimi/helmet/