. These exhibitions range from the dreadfully dull (tactical loudspeakers, new kinds of shipping containers) to the cutting-edge (exoskeletal power suits, robotic "mules" that follow soldiers like loyal dogs). Typically, reporters are welcomed to visit the booths, or even goaded into stopping by marketing personnel acting as carnival barkers. But every once in a while a company sets up a booth that just doesn't want the public's attention. Those are the places where I tend to linger.

At a conference discussing the present and future of military Special Operations, held in Washington, D.C., this week, I met a man single-handedly running a display booth vending surveillance equipment. His table of wares included ruggedized tracking devices, minuscule video recorders and audio bugs concealed as everyday items. The company sells snooping gear to law enforcement and military customers; no private clients ever see its technology, and it is bound by law not to sell to the public. Also on display were various specialty devices—1.5-inch-long audio recorders that can upload data remotely, soda cans that conceal high-frame-rate video cameras, vehicle trackers that attach to undercarriages with magnets, covert GPS antennas that can be integrated into a car's windshield, and so on.

Intriguing stuff, but would I be afforded a closer look? The man's face became pinched as he read my symposium-issued name card, hanging from a lanyard and festooned with a pink ribbon reading PRESS. "I'd love to talk about what we do," he said. "It's too bad I can't." Negotiations followed, and he agreed to talk to me—if I left out his company's name and kept him anonymous.

Normally I'd balk at such limitations, but as we jawed I realized that even such a sanitized conversation provides a glimpse into the niche world of covert operations marketing and supply. The company is built around secrecy, and maintains only about 20 employees. "This is entirely a word-of-mouth business," he says. "We don't advertise. We need to stay small and quiet."

Business doesn't usually come in the form of a written, publicly released Request for Proposal, as with other defense or government contracts. It starts with a phone call; a description of what's needed and a deadline for delivery. (They also have a catalogue for more common law enforcement products, like attachable audio bugs, encrypted data transmitters and 360-degree streetlight cameras.) The product is crafted entirely in-house.

The federal police use the devices to snoop on suspects, keep track of their agents or informants and gather courtroom-ready evidence. The targets are usually drug dealers, terrorists or organized criminals. Military operators use the devices to positively identify targets and gather intelligence and to support various diplomatic, training and development programs in host nations, the kind of nonviolent work that takes up so much Special Forces time and effort.

The police sometimes fill the company in on how products were used, but there is usually zero feedback on how it worked from military clients. "If something didn't work right, we'd hear about that," said the man in the booth. "Otherwise, we have no idea."

Many government clients want their own unique gear. Sometimes a customer sours on a product if it has been purchased by another U.S. agency, he says. For example, a sale of a pinhole video recorder with line-of-sight uplink capability to the Drug Enforcement Administration might turn off the Special Operations command, who want to buy something that has never been used before, and is therefore not likely to appear in a courtroom or foreign intelligence briefing.

I asked the man what the biggest trends are in this niche industry. Not surprisingly, he noted the shrinking size of electronics, snatching up a tiny video recorder from the table: it can capture 8 hours of evidence with a pinhole-size camera and can be stored in a wafer-thin, 2-inch-long data card the thickness of a driver's license. The recorder is one-third smaller than the company's earlier model, released just two years ago. The use of biometrics—identifying people by their physical features—has increased the demand for high-quality still images that facial recognition software can process. For example, the U.S. military keeps files on insurgents and terrorists for just such a purpose. Every frame of such a video has a high-enough resolution and clarity to be used to match faces and identities. Set up a clandestine video camera, find a known insurgent leader, positively identify him and order an airstrike or raid. Precision weapons only really work if you know who you are aiming at.

Audio recording is also improving. For example, the ability to record within a certain radius without also capturing ambient noise has increased reliability and customer interest. Mobsters who meet in crowded restaurants, convinced that the background chatter will make recordings indecipherable, are no longer safe. Interest in this improvement is especially high among law enforcement customers, since they cannot alter audio evidence to clear up the sound.

There is plenty of spy gear available on the open market—entire Internet sites are set up to vend them. But when an agent or military special operator is using gear during a life-threatening situation, there is no interest in finding an off-the-shelf product. Commercial surveillance gear is too flimsy to meet these demands, the man said. "I tell my customers to order that stuff, and then come back and talk to me in a week or two," he says. "Their devices are not built of extruded plastic, and they are not sealed well enough to keep out dust or moisture. They're just not rugged enough. You can run over ours with a car and it'll still work."

I told the man that his was a strange business. He agreed, and added that it can change someone's outlook. For him, vending hidden surveillance equipment, especially those items masked as everyday, changed the way he views the world. "Working in concealments made me paranoid," he says. "These things can be anywhere. I don't even pick my nose alone in an elevator anymore."

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