Many creatures have the ability to "steer" the pinnae of their ears in different directions to allow rapid focussing on different sound sources, and to aid their location. Some breeds of dog, antelope, and even horses have this facility, although in the case of horses the benefit is unclear; however
good the audio data, there's no actual brain there to process the input.
Humans can't steer their pinnae - they have to turn their head.
Now, it seems (based on a number of movies and TV shows) that humans frequently find themselves in threatening situations where someone or something is creeping up behind them. Sometimes, of course the threat turns out to be innocuous- another cop, a cat, a bird, or an injured victim.
It would be helpful in such situations to be able to select "forward" or "reverse" hearing.
So, simply don your BorgCo Earboosters (Patent applied for). Attached to an elasticated headband, the twin precision-engineered plastic sound reflectors fit neatly behind the existing ears, augmenting the volume of normal hearing. But simply twist the forehead-mounted control knob, and the cups instantly flip forward, like clamshell thrust reversers on a turbojet, reflecting sound sources behind the wearer in case of suspicious movement.
Requiring no power, and folding neatly away in a pouch when not required, this new product is an ideal gift for those enamored of exploring dark corridors in abandoned buildings, unlit passageways in derelict ships, or fog-filled graveyards on the edge of town where the hideously disfigured psychopathic killer is known to live.