Tin foil hat

The notion of wearing homemade headgear for such protection has become a popular stereotype and byword for paranoia, persecutory delusions, and belief in pseudoscience and conspiracy theories.

[1] Some people – "Tin Foil Hatters" – have a belief that such hats prevent mind control by governments, spies, mobsters, corporations, extraterrestrial, or paranormal beings that employ ESP or the microwave auditory effect.

People in many countries who believe they are "targeted individuals", subject to government, corporate, or criminal spying or harassment, have developed websites, conference calls, and support meetings to discuss their concerns, including the idea of protective headgear.

[9] In 1962, Allan H. Frey discovered that the microwave auditory effect (i.e., the sounds induced by the reception of radio-frequency electromagnetic signals, heard as clicks and buzzes) can be blocked by a patch of wire mesh (rather than foil) placed above the temporal lobe.

In a 2016 article, the musician and researcher Daniel Wilson writing in paranormal magazine Fortean Times noted an early allusion to an "insulative electrical contrivance encircling the head during thought" in the unusual 1909 non-fiction publication Atomic Consciousness[15] by self-proclaimed "seer" John Palfrey (aka "James Bathurst") who believed such headgear was not effective for his "retention of thoughts and ideas" against a supposed "telepathic impactive impingement".