California residents who lit illegal fireworks over the July 4 holiday may be in for a nasty surprise in the mail thanks to covert fire department operations.

A number of California cities, including Sacramento, have begun using drones to locate people shooting off illegal fireworks. From Wednesday to Saturday night, the Sacramento Fire Department’s special fireworks task force patrolled the streets with unmarked cars and drones, focusing on neighborhoods where they’ve had prior complaints. Task force officers and the drones took photos of the illegal activity, and within 30 days the property owner where the fireworks were used could receive a fine in the mail.