A recently declassified US Army report on the biological effects of non-lethal weapons reveals outlandish plans for "ray gun" devices, which would cause artificial fevers or beam voices into people's heads.

The report titled "Bioeffects Of Selected Nonlethal Weapons" was released under the US Freedom of Information Act and is available on this website (pdf). The DoD has confirmed to New Scientist that it released the documents, which detail five different "maturing non-lethal technologies" using microwaves, lasers and sound.
Released by US Army Intelligence and Security Command at Fort Meade, Maryland, US, the 1998 report gives an overview of what was then the state of the art in directed energy weapons for crowd control and other applications.

A word in your earSome of the technologies are conceptual, such as an electromagnetic pulse that causes a seizure like those experienced by people with epilepsy. Other ideas, like a microwave gun to "beam" words directly into people's ears, have been tested. It is claimed that the so-called "Frey Effect" – using close-range microwaves to produce audible sounds in a person's ears – has been used to project the spoken numbers 1 to 10 across a lab to volunteers'.

In 2004 the US Navy funded research into using the Frey effect to project sound that caused "discomfort" into the ears of crowds.
The report also discusses a microwave weapon able to produce a disabling "artificial fever" by heating a person's body. While tests of the idea are not mentioned, the report notes that the necessary equipment "is available today". It adds that while it would take at least fifteen minutes to achieve the desired "fever" effect, it could be used to incapacitate people for almost "any desired period consistent with safety."

Less exotic technologies discussed include laser dazzlers and a sound source loud enough to disturb the sense of balance. Both have been realised in the years since the report was written. The US army uses laser dazzlers in Iraq, while the Long Range Acoustic Device has military and civilian users, and has been used on one occasion to repel pirates off Somalia.

However, the report does not mention any trials of weapons for producing artificial fever or seizures, or beaming voices into people's heads.