In Charlottesville, police officers are prohibited from using in criminal cases any evidence obtained by drones, also known as unmanned aerial vehicles. Never mind that the city police department does not have a drone, nor has it suggested buying one. The police are not barred from using drones for other efforts, like search and rescue.

Mr. Norris said the advent of new policing technologies poses new policy dilemmas for his city.

Charlottesville permits the police to install cameras temporarily in areas known for drug dealing, but it has rebuffed a police request to install cameras along its downtown shopping corridor. It has also chosen not to install cameras at traffic lights to intercept speeding cars, as is common elsewhere.

“Drones are capable of taking surveillance to a whole new level,” Mr. Norris said.

Last week, the Seattle Police Department agreed to return its two still-unused drones to the manufacturer after Mayor Michael McGinn answered public protests by banning their use. On Thursday, the Alameda County Board of Supervisors in Oakland, Calif., listened to the county sheriff’s proposal to use federal money to buy a four-pound drone to help his officers track suspected criminals — and then listened to raucous opposition from the antidrone lobby, including a group that uses the Twitter handle @N.O.M.B.Y., short for Not Over My Back Yard.

This week, members of Congress introduced a bill that would prohibit drones from conducting what it called “targeted surveillance” of individuals and property without a warrant.

A federal law enacted last year paved the way for drones to be used commercially and made it easier for government agencies to obtain them. The Department of Homeland Security offered grants to help local law enforcement buy them. Drone manufacturers began to market small, lightweight devices specifically for policing. Drones are already used to monitor movement on the United States’ borders and by a handful of police departments, and emergency services agencies around the country are just beginning to explore their uses.