Hard sound rifle

A Hard Sound Rifle is a Human-made sonic weapon. As it utilizes concentrated sound waves instead of a solid projectile, a hard-sound rifle kills instantly and leaves no residue or powder burns and causes little noticeable external damage to the intended target, making the weapon virtually untraceable in forensic investigations. A preferred weapon used by assassins of the Office of Naval Intelligence, they are sometimes (illegally) purchased by civilians, for less malevolent means. The Hard Sound Rifle can be used as a more efficient, and more stealthy version of a sniper rifle.

Although sonic weaponry doesn't appear in all three Halo games, it is mentioned prominently in I Love Bees. When an ONI assassin, disguised as a homeless man was sent to kill Rani Sobeck for her investigation into a covert evacuation of the human colony of Troy, a protective detail dispatched by Colonel Herzog eliminated the operative through use of a hard-sound rifle. Having fallen off the roof to the street below, local authorities dismissed the death as an accident resulting from use of alcohol or drugs.