The Directional Resonance Guns (指向性共振銃, Shikōsei Kyōshin Jū?) is a type of specialized gun.
It is still unknown where it came from.
They are guns used against ability users. It produces a sound wave which directly shakes up the brain, causing a loss of consciousness in one second and death in ten seconds 
- Bungo Stray Dogs Manga: Chapter 72.