A "hair streamer" isn't a commonly used term in the hair care industry. It's possible that you may be referring to a "hair steamer" or a "hair vaporizer," which are devices used in hair care treatments to infuse moisture into the hair and scalp. 
A hair steamer typically consists of a base unit with a water reservoir and a hood or cap that fits over the client's head.
The hood may be adjustable in height and can often be rotated to ensure even distribution of steam to all areas of the hair and scalp.