When I was a kid, it was easy to tell who the geeks were. They were the kids wearing pocket protectora in their shirt pockets.

Well, times have changed. The slide rule and pocket protector are gone, and the cool kids are carrying pocket projectors, not pocket protectors.

This new class of device, many of them about as small as a deck of playing cards, thinner than a pack of cigarettes, was all over the place at the Consumer Electronics Show in Las Vegas in January.

Many were promised with spring ship dates. And now that spring has sprung, we should expect them on store shelves and at online merchants any day.

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The pocket projector results from two developments. On the technology side, it's the development of two projection-display technologies originally intended for big-screen televisions.

Texas Instruments developed the DLP chip for large-screen displays, using a rear-projection technology, which a couple of years ago we saw in a host of big screen HDTV's.

At that time, the technology was less expensive than large-screen plasma and LCD displays. But now that those technologies have dropped in price, DLP has fallen out of favor.

DLP actually uses deformable microscopic mirrors in the image creation process. A competing technology, liquid crystal on silicon, or LCoS, was also created for large-screen projection devices, but failed to catch on.

Both technologies effectively were made obsolete by the dropping prices for LCD and plasma screens. Now both have found a new lease on life in pocket projectors.

The other impetus for the development of pocket projectors was the sudden explosion in personal video players, especially Apple's iPod. But there are a host of other small screen devices from Creative, SanDisk, Microsoft and others.

Pocket projectors make it easier to view movies from these devices in places like a dorm room, a hotel room, or even on the back of an airline seat.

After all, a two inch screen really does have its limitations, especially after you've been watching your favorite movies and television shows at home on a 50-inch or 60-inch screen.

Most of the pocket projectors use the DLP Pico chip from Texas Instruments, and many of the devices actually use the name of the chip.

Among them is one of the first shipping units, the $399 Pico PK-101 from Optoma. Battery life on the Optoma is about an hour and a half, just as advertised. For the serious user, you might take along an extra battery.

The image is viewable at any range from 10 inches to about 10 feet, though the brighter the room and the less white the projection surface, the more the 480x640 image will fall apart.

The Pico chip is also in models from Toshiba, and Samsung. Toshiba's Pico, also expected at $399, is due to ship in the second quarter.

The pre-production model we saw wasn't quite this sleek but had the same innards, which were about identical to those of the Optoma (I think they may have come from the same assembly line) .

Toshiba also has another DLP projector, the TDP-F10, a larger, boxier version which is suitable for room-sized presentations.

But unlike the smaller Pico projectors, it's not battery-powered and is more like a scaled-down version of more traditional projectors.

It uses a standard VGA cable input, and has a considerably brighter and sharper image than the pocket-sized versions. Due to ship in April, last we heard pricing might be anywhere from $499 to $599.

As noted, the resolution on the pocket projectors is VGA quality, so it's clearly not a thrilling cinematic viewing experience. But it gets the job done if you understand its limitations. This is really for either personal viewing or a small circle of friends.

Battery life is limited. Most use a universal USB charging cord. They come with a variety of available connectors, including a standard AV-to-video out. Some come with iPod adapters.

Audio is handled by a separate channel. The devices I saw all had built-in speakers that were hardly worth bothering with.

Headphones are far more useful. You can also use the headphone connector on your iPod to drive external speakers.

Some, like the Optoma, come with an adapter so you can mount the projector on a desktop tripod.

The Z10 unit from Nextar, which uses LCoS, not the TI Pico chip, comes with its own tripod and has an available screen. Expected price is $299. The portable screen is an extra $39.99.

Toymaker WowWee is bringing out a version called the Cinemin Swivel that allows you to tilt part of the projector 90 degrees to show movies on the ceiling. Trust me, this is useful.

The technology is on its way in a variety of packages. Samsung is brining one to market that combines the Pico projector with a cell phone, but so far the company only intends to market it in Korea.

Toymaker Jakks Pacific is bringing out a low-cost version to market called the EyeClops mini, which it expects to sell for under $100.

This is only the start of the list. It seems like everybody and his brother is jumping into this market, including 3M, Microvision, Aiptek, Aaxa, Epoq, Beambox and Samsung. Makes you wonder if anyone will get enough appreciable market share to make it all worthwhile.

The bottom line on these is that they are fun. They do have a use. But the "wow" factor probably outweighs the "useful" factor.

They can be used to do a desktop presentation off your computer to a group of three or four. They're fine for watching a movie on the ceiling in a dark hotel room.

But even though more than dozen companies are bringing them to market, It's unclear to me just how much of a market there's going to be.

Sure, I love traveling with the Optoma and pulling it out of my knapsack, hooking it up to my iPod and saying, "hey, get a load of this".

Though on my Metro North commute, you'll find me watching a movie on my Vuzix glasses as I cocoon with my hood pulled over my head, or on the Archos media player.

But next week, I'll try projecting the Optoma onto an airplane seatback. It's got to be better than the cabin movie anyway.