White noise machine

A white noise machine is a device that produces a sound that is random in character, somewhat like air escaping from a balloon. They generally do not produce actual white noise, which has a harsh sound, but more often pink noise, whose power rolls off at higher frequencies, or other colors of noise.

Use
They are often used to protect privacy by masking distant conversations, say in a psychiatrist's waiting room, and are also sold as sleep aids. Such machines often can produce other soothing sounds, such as rain, wind, and ocean waves. They are often used by sufferers of tinnitus to mask their symptoms.

Studies have shown that employing white noise machines in offices improves productivity by reducing distractions.

Mechanics
Simple machines consist of a very basic setup, involving an enclosed fan and (optionally) a speed switch. This fan drives air through small slots in the machine's casing, producing the desired sound. More complex machines may be electronic, and offer a variety of 'nature sounds' in addition to white noise.

Manufacturers recommended that the volume of white noise machines be initially set at a comfortable level, even if it doesn't provide the desired level of privacy. As the ear becomes accustomed to the new sound and learns to tune it out, and the volume can be gradually increased to increase privacy.