A Brooklyn high school confiscated 21 weapons just one day after metal detectors were installed.

City officials installed metal detectors at Urban Assembly School for Law and Justice Thursday morning after a 17-year-old student was caught with a pistol and more than $30,000 in cash. It only took one day for the school's faculty to confiscate an arsenal of weapons that included nine knives, seven cans of pepper spray, four stun guns, and a pair of brass knuckles.

The 17-year-old, who was caught with the gun and cash, was busted after showing up late and logging his attendance in the office. A secretary alerted school safety agents after seeing what she believed was a gun in the student's backpack. The student was detained until NYPD arrived and discovered the items. As a result, the student was arrested and taken to a local precinct.

Mayor Bill de Blasio increased unannounced scanning in schools this year due to various gun seizures and violent incidents occurring in the city's schools.