They’re small, inexpensive and capable of feats that once belonged to the realm of science fiction — and they’re here to stay. The advent of drones is one of the most significant technological advances of our time.

These pilotless, remote-controlled aircraft have been a boon to the war against terrorist enemies in South Asia. They were a key to our successful intervention in Libya. With great promise for law enforcement, they also have been deployed by the Department of Homeland Security to detect people illegally crossing this nation’s southern border.

As the recent filibuster by U.S. Sen. Rand Paul, R-Ky., dramatized, however, these machines also evoke serious concerns. In the realm of the war on terrorism, the fear is that, having been used on foreigners and even American citizens involved with al-Qaida, they may be used to kill Americans on U.S. soil without a hearing or trial.

“The Fifth Amendment protects you … from a king placing you in the tower, but it should also protect you from a president that might kill you with a drone,” Paul said.

Most police agencies in the U.S. haven’t been rushing to adopt drones, but they have been put to use by police departments in Miami, Seattle and Little Rock, Ark. Civil libertarians fear surveillance drones will become so common that even law-abiding citizens will find it impossible to escape the unblinking eye in the sky.

The warnings are not baseless. The Obama administration has needlessly fueled the worst suspicions with its secrecy about its policy in using drones against enemies.

Only recently did it make public a Justice Department white paper — and then only after the document leaked to the media. And the White House has yet to fully disclose the legal basis for its actions.

The rules, however, are not expansive — limiting targets to senior figures in al-Qaida and affiliated groups who are involved in planning attacks and cannot be captured.

This last condition, Paul might have noticed, would exclude almost anyone on U.S. soil, citizen or not, since apprehending a suspect here is far easier than in Yemen or Somalia.

It was nonetheless reassuring to hear the admission that Paul finally coaxed from Attorney General Eric Holder, who said the president does not have the right to use a drone to kill an American “not engaged in combat” in this country. Only in extraordinary circumstances is it possible to imagine such use — say, a citizen working for al-Qaida who hijacks a plane and steers it toward a skyscraper.

As for police drones, it’s not too early to start talking about how they may be used to enhance public safety without violating individual privacy. Because of their low cost, quiet operation and maneuverability, drones could be a great boon to crime fighting, letting cops monitor criminals far more intensively than they can today.

For the same reason, however, they could significantly impinge on privacy.

The American Civil Liberties Union of Illinois wants the General Assembly to limit their use to a few purposes, such as preventing a suspect from escaping, locating missing people and averting imminent harm to life or property. Aside from those circumstances, police would need a search warrant.

Police and prosecutors may argue that drones are technologically different — but their deployment not terribly different in principle — from helicopters, cruisers and fixed cameras that allow police officers to monitor citizens.

Drones are clearly a big part of the future. Now is a good time to address what that future will be.

Editorial by the Chicago Tribune