An Arizona company developing a new type of high-altitude, long-range surveillance platform just completed a 16-day mission during which massive balloons floated over four western U.S. states, all part of an effort to someday keep them aloft for months at a time.

World View Enterprises Inc. builds what it calls Stratollites, a system designed to offer the type of coverage satellites afford but without the need to launch incredibly expensive rockets into space. Effectively unmanned balloons, the platforms operate with surveillance equipment payloads of as much as 220 pounds (100 kg) at altitudes of 50,000 feet to 75,000 feet, far above commercial air traffic.

They will be able to monitor mines, pipelines, transit infrastructure—and perhaps the contents of your fenced-off backyard—in hyper-accurate detail.

The company plans to start selling its commercial product early next year and has spoken with several potential commercial and military customers, Chief Executive Officer Ryan Hartman said Tuesday in an interview. World View sees its customer base as companies that operate critical industrial and commercial infrastructure.

The mechanism can provide imagery that’s superior to orbiting platforms, Hartman contends, because “we’re five times closer to the earth than the nearest satellite.” He said “our imagination is sort of our limit with regards to where and how these systems can be used. Certainly there is a market in target surveillance and reconnaissance on a global scale.”

“There’s a very real potential here that these kinds of systems will lead to a pervasive aerial surveillance.”

Given that satellites have the capacity to read license plates, World View’s product may have implications for privacy and civil liberties. Asked if the company would sell access to police departments, Andrew Antonio, director of business development for World View, said “flying a Stratollite is no different” than how “domestic law enforcement agencies leverage aerial technologies like helicopters and aircraft.”

Jay Stanley, a senior policy analyst with the American Civil Liberties Union, isn’t so sure.

“Everything depends on how expansive it is and how high resolution it is and how wide of an area it can surveil,” Stanley said of World View’s Straollite. “There’s a very real potential here that these kinds of systems will lead to a pervasive aerial surveillance of cities where our every move will be tracked.”

He pointed to a sweeping 2012 ruling by the U.S. Supreme Court that limited police power to track people using GPS devices. The reasoning used by some of the justices in that unanimous ruling could easily be expanded to other types of surveillance technology, Stanley said.

Jeramie Scott, senior counsel for the Electronic Privacy Information Center’s Domestic Surveillance Project, said that while high-altitude surveillance balloons may have beneficial uses, “they will also pose a serious threat to our privacy and civil liberties.

“The balloons will likely drive down the cost of surveillance, making persistent aerial surveillance of all our public movements a real possibility,” Scott said. “Traditionally, our privacy in public has been protected by the limitations of technology and the exorbitant costs of tracking everyone’s public movements, but surveillance balloons potentially remove these barriers.”

World View’s own test showed that the ability for surveillance technology to linger overhead for long periods of time, covering a wide swath of America, is indeed in reach.

The company’s 16-day test flight started near the company’s Tucson headquarters and spanned more than 3,000 miles over Nevada, Utah and southern Oregon, ending Monday in the Nevada desert. The company said it plans to extend its next test flight to 30 days, and then 60 days.Several satellite firms do offer similar data to a range of clients, from agriculture to meteorologists to hedge funds. Meanwhile, Alphabet Inc.’s Project Loon also uses balloons in the stratosphere, designed to provide Internet and communications services. The company said it’s worked with AT&T Inc. and T-Mobile US Inc. to provide infrastructure to Puerto Rico following its devastation by a hurricane.