Ask your Internet search engine to look up “drone” and you will find that the word comes from an Old English word for male bee, and is onomatopoeic. It has also been used to denote idle men, like the pampered denizens of P.G. Wodehouse’s fictional Drones Club in London’s Mayfair district. And it describes the groaning noise made by a bagpipe. It is only in recent years that the word has acquired ominous overtones from its application to lethally armed military unmanned aircraft with names like “Predator.”

Perhaps it was the use of Predators as assassination vehicles by the CIA and Pentagon that raised an alarm when FBI Director Robert Mueller recently said that his agency uses drones in investigations, although sparingly. The Department of Justice says the Drug Enforcement Agency and the Bureau of Alcohol, Tobacco, Firearms and Explosives also use drones. Apparently none is armed. It should stay that way.

The news upset Sen. Dianne Feinstein, D-Calif. “The greatest threat to the privacy of Americans is the drone and the use of the drone, and the very few regulations that are on it today,” she said.

But Ms. Feinstein heads the Senate Intelligence Committee, which oversees the National Security Agency and its vast surveillance programs that have recently become the legitimate subject of privacy concerns. She approves of the NSA programs so her cry of alarm about drones seems oddly inconsistent. Unless, of course, she is trying to change the subject.

In any event, it is clear that the day of the drone—meaning a small unmanned flying vehicle — has arrived. As has the era of “big data” that allow companies to look over your shoulder as you cruise the web.

On the Internet you will find many remote-controlled flying vehicles for sale at prices ranging from several hundred to several thousand dollars. Click on one of these offers, and odds are ads for this product will begin to crop up on your web pages. Someone, or more likely some computer program, has noted your interest in drones and now your Internet Service Provider is selling ads targeted at you.

You may also reasonably worry that your on-line query has been swept up by the NSA and lies there in its vast archive, waiting for an investigator who has been tasked to look at all communications using the word “drone.”

Now maybe your neighbor has bought a drone and is using it to peer over your backyard fence where you are sunbathing. Invasion of privacy? That’s tough to prove when the sky above your abode is crisscrossed daily by police helicopters, private aircraft, scheduled airliners, assorted military aircraft and even satellites that can read a license plate number from space. All of them can look down on your yard.

Drones and “big data” are whittling away at our zones of privacy and we seem to have few defenses. It is time Congress paid attention to the issues they raise.