Active shooter drills do not use gunfire.
Some do use noisemakers and special .223 paintball rounds that work in the patrol rifles with a special bolt to allow the rifle to function semi-auto with the reduced recoil of the paintball rounds.
However, I can’t see an exercise happening without all LEO knowing it’s going on. Typically, many surrounding depts that would be providing assistance for the real thing will be invited to come and train so Officers can learn each others buildings, some are real mazes.