This provision is a "subjective immission" control with a curfew. It has been used to regulate the sound of model aircraft on both private and public property. It applies to airborne, water-borne, and land-borne, unmanned vehicles. It makes no distinction between model vehicles and full-size unmanned vehicles. it applies also to the engines of those vehicles. Most regulations pertained to private unmanned vehicles, normally restricted to local open fields. The development of drones with microphones, cameras and GPS has opened the door to commercial use over wider private and public properties. Since federal preemption of drone use will likely occur, it is important for this provision to make the distinction. Salt Lake Health Department (Section 4.5.15) limits activity to 800 feet from a dwelling between 10 pm and 7 am, or if it cases a noise disturbance. Atlanta, GA (Section 74-136(b)) uses the "plainly audible" criterion across a residential property line, on a public property from 10 pm to 7 am on weekdays or from 10 pm to 10 am on weekends or holidays for any sound source.