Adapted from the Web page:

AutoZen generates sounds meant to cause the user's brain waves to
shift to a different dominant frequency, resulting in an altered
state of consciousness.  If you are under treatment for any
psychiatric or neurological disorder, you might want to approach
this with caution.  You must use headphones for AutoZen to work at
all.  The effect depends on each ear receiving a different tone,
and the combination of the inputs in the brain.  If you are deaf
in one ear, it will not work.

WWW: http://www.linuxlabs.com/autozen.shtml