(FORTUNE Magazine) – A CIA PREDATOR DRONE, AS USED IN AFGHANISTAN AND Iraq, costs $25 million, not that you could buy one even if you could afford it. But the Draganfly Predator is another matter. It's a scaled-down model of the real thing (wingspan: six feet instead of 49 feet), and like its namesake it carries a video camera and is controlled by radio from the ground. It can climb to 8,000 feet and can cruise lazily in the sky for up to an hour and a half, transmitting full-color video all the while. The drone is quietly battery powered, so if one were circling above your house or office or your kids' school right now, probably no one would notice. And it costs not $25 million, but just $750.

You already know you're being watched more and more all the time. But if you're like most of us, you don't realize how stunningly fast the advance of sensor technology, software, and the Internet is enabling someone, somewhere, to capture virtually every aspect of your existence. The developed world now consists of two groups. A small minority of techies are so familiar with the galloping increases in computing power and decreases in component size that nothing shocks them. They find the Draganfly Predator a big yawn compared with what they know will be available in two years. The other group, the vast majority, has only a hazy idea of the astonishing new ways in which their lives can be X-rayed, and finds most of them incomprehensible. So at just the moment when technology's power to peek is mushrooming, not many people can be bothered to worry about it.

Of course plain old optical surveillance, as offered by the Predator, is so omnipresent we scarcely notice it, though its extent has become breathtaking. An estimated four million surveillance cameras watch Britain; that's more than six for every square mile. Monaco brags that literally every square inch of the principality is now under 24-hour government video surveillance. Most surveillance cameras in the U.S. are private, so keeping track of them is tough. A group in New York City runs a website with hand-drawn maps of their locations around town; the group counted 284 in a small area of Midtown last year, for example.

But surveillance cameras rarely see the most valuable information about you. That's obtained in ways that are much harder to detect. If you have a computer at home and you aren't a dedicated geek, for example, chances are excellent that your machine is infected with spyware, software that automatically sends some of your data to somebody else.

RFID (radio frequency identification) tags are on millions of pallets of consumer goods and will eventually be on individual items, identifying each one uniquely. If you buy with a credit card, a record linking you to that specific item will be in a database. These tags are often attached so they can't be removed without destroying the item, and in any case you can barely see some of them; the smallest are the size of a grain of salt. They can be read invisibly from up to 30 feet away. So someone you don't know and can't see, with a tag reader and access to the right database, could read the tag in your shirt or wallet or shoes and suddenly know a great deal about you.

Much more is happening. Many kids across America now get their school lunch every day by putting a thumb or finger into a scanner--quick and convenient, but how secure are your kids' fingerprint scans, which will identify them for life? Microsoft's prototype SenseCam hangs around your neck or can be concealed in jewelry, and takes a digital picture whenever it detects a change in light, motion, or temperature, up to 2,000 images a day; now imagine what happens when the company adds face-recognition technology and broadband connectivity, as it hopes to, and everyone on the street is wearing one.

The observations here reflect only technology that's available now, not even beginning to imagine what will exist in a few years. And while the possibilities are alarming to some, we shouldn't conclude that a Big Brother scenario necessarily awaits us. We truly don't know. Some futurists even argue that utter data transparency--everyone knowing everything about everyone else--offers citizens their only defense against increasingly data-rich institutions.

What we know for sure is that we have no excuse for waking up one day to find that every fact about our physical, financial, mental, and emotional lives is available to others. The amazing technology making all that possible is being developed right now--in plain sight.

GEOFFREY COLVIN, senior editor at large of FORTUNE, can be reached at gcolvin@fortunemail.com. Watch him on Wall $treet Week With FORTUNE, Friday evenings on PBS.