Ever since the U.S. government began using unmanned drones to track and kill suspected terrorists in remote regions of Pakistan, the prospect of their widespread use domestically seemed like a remote possibility. For one thing, in the minds of much of the American public, drones are weapons—the equivalent of flying bombs. For another, their use has sparked widespread criticism at home and abroad.

Congress, however, wasn’t much concerned about drones’ image problems. It passed a little-noticed bill in 2012 (signed by President Barack Obama) that clears the way for and encourages the use of drones, albeit in a more benign manner than they are used to target Islamic radicals. With the passage of the bill, the Federal Aviation Administration (FAA) estimates that more than 30,000 drones, some operated by law enforcement and others by private companies, could be inhabiting American airspace by 2020.

As with other rapidly advancing technologies such as mobile phones and GPS, the state of the law isn’t keeping pace with privacy concerns. The drone legislation passed last year does nothing in terms of protecting the rights of those who may fall within the sights of a hovering drone. Indeed, it doesn’t speak to them at all. And the law tasks the FAA, an agency that has a much greater level of comfort ensuring air safety than safeguarding constitutional rights, with regulating domestic drone use. Wells Bennett, a lawyer and analyst for the Brookings Institution in Washington, D.C., says the issues that the FAA must resolve in the coming years are "gargantuan."

Fear of government overreach is one thing that can still unite watchdogs on the left with libertarians on the right. In mid-December Representative Edward Markey (D-Massachusetts), who is seeking to replace John Kerry in the Senate, introduced a bill that would amend the drone law to limit collection of private data, and would require law enforcement agencies to obtain a warrant before using drones for surveillance. It would also force operators of the crafts to disclose how the drone will be used, what kind of information will be collected, and whether it will be sold to third parties. The current law is silent on all of these aspects.

The Markey bill is similar in some respects to one offered earlier last year by Representative Ted Poe (R) of Texas. A former Houston prosecutor and judge, Poe held a congressional hearing last fall in Houston—an aerospace hub—to address Fourth Amendment concerns related to drones. Calling his bill a starting point, Poe urged Congress to act in the privacy sphere rather than wait for federal courts to sort it out when the inevitable lawsuits roll in. "We must decide now when drones can and cannot be used in order to ensure our constitutional safeguards," he said.

The top Democrat on the House Judiciary subcommittee that Poe chairs, Representative Hank Johnson of Georgia, was more direct about his worries. "We’re not a nation of suspects," Johnson declared at the hearing. "As the number of drones rises, so, too, will the number of suspects. These suspects could be lawful demonstrators or a person lawfully driving along a highway within 20 miles of the border."

In fact, U.S. Customs and Border Protection has been using drones for several years to track illegal immigration and drug smuggling. And now some police departments and sheriff’s offices are looking to become early adopters of drones in policing. In December an outcry from privacy groups convinced Alameda County in Northern California to hold off on purchasing a drone for law enforcement. While the county insisted that the drone would be mainly used for search-and-rescue operations, an internal memo from the sheriff’s department obtained by local activists suggested that it could also be used for "investigative and tactical surveillance, intelligence gathering, suspicious persons, and large crowd-control disturbances."

The nonpartisan Electronic Privacy Information Center estimates that over 60 counties and municipalities nationwide have already been approved by the FAA to operate drones, and, the center claims, some law enforcement agencies are interested in outfitting them with lethal or nonlethal weapons.

Regardless of whether drones in the United States will be weaponized, they are becoming increasingly sophisticated. Equipped with such features as long-range and night vision cameras that can pick up license plate numbers, see-through imaging similar to that used by body scanners employed at airports, and face recognition software that is tied to federal data­bases at the U.S. Department of Homeland Security and the Federal Bureau of Investigation via Wi-Fi, drones’ technological capabilities have led groups such as the American Civil Liberties Union to complain that they are ripe for abuse.

Perhaps more chilling, civil liberties groups point out, is that drones, which are relatively cheap to produce, can erase the practical limits placed on other forms of aerial surveillance. "Small, hovering platforms can explore hidden spaces or peer in windows, and large static blimps enable continuous, long-term monitoring—all for much less than the cost of a helicopter or plane," ACLU’s counsel Christopher Calabrese told Poe’s panel.

Supporters argue that drones can do work better suited for robots than people, such as flying into hurricanes and forest fires. Brookings’s Bennett, for one, says that while the concerns of privacy groups are legitimate and merit "sober contemplation," the benefits are too good to pass up. "The upsides are big. They have a lot of applications in the disaster relief setting, environmental mapping, and [monitoring] traffic patterns," he says. "There is a lot you can do with less money and less danger to people than you could do otherwise."

The FAA has been directed to have a working regulatory regime up and running in two years, and it remains unclear to what extent the agency can, or will, take privacy concerns into account. Still, if Congress doesn’t act within that time to clarify the state of the law, the courts will be forced to referee.

The U.S. Supreme Court has previously sanctioned aerial surveillance without a warrant, concluding that if contraband such as marijuana plants lies in plain view of an aircraft, then the Fourth Amendment is not implicated. But the enhanced detection capabilities of drones likely renders that decision less than instructive.

A case involving the use of a GPS tracking device decided by the court just last term suggests a thicket of technology-versus-privacy concerns that awaits any judge who weighs in on drones. While a majority of justices held that the suspect’s rights were violated because police committed a physical intrusion by placing the device on his car, others said that the court missed the point entirely. "Physical intrusion is now unnecessary to many forms of surveillance," warned Justice Sonia Sotomayor, adding that the threat of monitoring from afar has constitutional, as well as societal, implications. "Awareness that the government may be watching chills associational and expressive freedoms. And the government’s unrestrained power to assemble data that reveal private aspects of identity is susceptible to abuse."

Justice Samuel Alito, too, called for new guidance from Congress. But given the institution’s incipient paralysis (witness the fiscal cliff), the complexity of the issues involved, and even the presence of interest groups (drones already have their own Washington trade association that includes giants such as Raytheon Company and Lockheed-Martin Corporation), a fix may be long in coming. By then, Big Brother may have already taken wing.