IN JUNE a search-and-rescue team in Colorado used a drone to spot lost hikers in a pine forest, shaving hours off the time it would have taken to find the hikers using dogs, and thousands of dollars off the cost of doing so with a helicopter. In August police officers in Maine used a drone to snap 81 photos of the aftermath of a collision between a pickup truck and a blueberry lorry. The process took 14 minutes, instead of the hours officers said would usually have been required. Last month, police officers in Illinois used a drone to fly a mobile phone into the hands of a disgruntled man who shot at them when they tried to evict him from a foreclosed home. After hours of negotiations via the drone-delivered phone, they coaxed him into surrendering.

Despite such stories, many people are sceptical about the merits of law-enforcement drones. On September 28th Los Angeles’s Sherriff Civilian Oversight Commission, a body created a year ago by Los Angeles County officials to increase the accountability of its Sheriff’s Department, asked the department permanently to ground its drone, because of worries about privacy and safety. Such concerns have a basis in recent history. In 2012 the Los Angeles County Sheriff’s Department (LASD) secretly tested an aerial surveillance programme over Compton, a deprived neighbourhood in Los Angeles—though with a small aeroplane, not a drone.

Anxiety about drones is not confined to southern California: Seattle cancelled its drone programme in 2013 after residents and privacy activists protested, fearful of mass surveillance. A survey conducted in January by Rasmussen Reports, a polling group, found that 39% of American adults opposed the use of police drones compared with 36% who favour them.

Such tensions are set to intensify as an increasing number of law-enforcement agencies, fire departments and emergency-response teams start to use drones. A recent report by the Centre for the Study of the Drone at Bard College shows that at least 347 such departments acquired drones between 2009 and 2017. More drones were bought in 2016 than in all previous years combined, says Dan Gettinger, the study’s author. The buying spree shows no sign of slowing.

Growing recognition of how useful such machines can be is one reason for the rapid increase; another cause is the proliferation of affordable, easily operated consumer drones. The first police departments to adopt drones, in the mid-2000s, leaned towards buying expensive commercial drones that were produced specifically with law-enforcement and military applications in mind. But today many police, fire and emergency-response departments are opting for drones that are intended for use by photographers and hobbyists. Of the 315 departments for which the Bard College centre has drone-type data, 252 have at least one drone manufactured by DJI, a Chinese firm which is the world’s largest dronemaker. Its popular Phantom drones start at $499. Older models can be purchased even more cheaply on third-party websites.

The loosening of regulations by the Federal Aviation Administration (FAA) has resulted in more drone use by first responders. Before August 2016, all non-hobbyist drone operators had to hold licences to fly manned aeroplanes, too. Now there is a separate licensing process for operators of remote-controlled vehicles. Like private drone operators, police, fire and emergency-response departments are still bound by other FAA rules. They must register all their drones and are banned from conducting night-time operations (unless they have a special waiver) or missions where the operator loses sight of the drone that he or she is controlling.

On top of these federal rules, states are also putting limits on how drones can be used by law-enforcement agencies. According to the National Conference of State Legislatures, a bipartisan research group, 18 states require such agencies to seek search warrants before using drones for surveillance purposes.

Workers and drones

Some concern about government agencies’ use of drones is justified. But overly broad restrictions on their use could stop them from doing useful things such as monitoring crowds at concerts or marathons, which are public anyway. In a paper published in the George Washington Law Review in 2016, Gregory McNeal of Pepperdine University argued that, “legislation that requires warrants for drones treats the information from a drone differently from information gathered from a manned aircraft, by a police officer in a patrol car, or even an officer on foot patrol.”

Under the Fourth Amendment, he continued, police are not required to ignore wrongdoing until they have a warrant. “Why impose such a requirement on the collection of information by drones?” Instead, legislators might consider extending property owners’ rights to a certain altitude above their homes (Mr McNeal suggests 200 feet, or about 60 metres) and requiring that data collected by drones must be deleted after a certain period.