I ended up evaluating both the <a href="http://celluon.com/products/laserkey.ht ... 1">Celluon
Laserkey CL800BT</a> and the <a href="http://www.itechdynamic.com/en/products ... 10">I-Tech
Virtual Keyboard</a>. My overall impression is that unless you're desperately in need of zero-force typing, neither projection keyboard is an adequate substitute for a "normal" PC keyboard. However, the I-Tech ends up being the more functional device.
Both keyboards use the same technology. The keyboard image is projected onto a flat surface using a laser mounted at the top of the device. An infrared light source is emitted from the middle of the device. At the very bottom is a sensor that detects the infrared light reflected off your fingers as you type, allowing it to determine what key you pressed. Both devices allow you adjust sensitivity, or how close your finger gets to the surface before the device registers a key press. Both devices can detect simultaneous key presses as long as the fingers pressing both keys are visible to the sensor, which are the vast majority of combinations. The brightness of the projected image can be adjusted on both devices. However, neither device allows you to change the projected image itself.
At 11.5", the width of I-Tech's projected image is about the same as a normal full-sized keyboard. At only 9.5", the width of Celluon's is almost too small and cramped to use. The heights are both about 4", although Celluon squeezes in a sixth row for application keys, making the remaining rows even smaller.
Despite its small size, Celluon's layout is closer to that of a normal keyboard, and is therefore a little easier to get used to than the I-Tech. However, a huge caveat is that the Celluon device has no ALT key! I was so confused by this, especially since the left-hand side has plenty of room for an extra couple keys, that I emailed Celluon, asking where the ALT key was. They confirmed that the CL800BT has no ALT key, but the CL850BT coming out in a few months might have one. I'm not holding my breath.
The I-Tech takes more liberties with re-arraigning keys to fit in the trapezoidal projection area, especially with the punctuation keys, half of which are on the opposite side from their original positions. The SHIFT keys are also resized and placed so far to the sides that they're very hard to reach without moving your fingers from the home row.
I would have posted a picture, to help illustrate their layouts, but the brightness of the laser light made the image come out far too blurry to be useful.
Even though both devices require special drivers for configuring on-board settings like key sensitivity and projection brightness, the I-Tech supports the Bluetooth HID interface, allowing basically any platform that supports Bluetooth to use it as a keyboard (including Linux). The CL800BT only supports SPP, requiring a custom driver for each platform.
The I-Tech has a built-in beeper to simulate a key press "click". The Celluon uses the host's speakers to produce a click sound by playing a wav file. This also gives you the freedom to use a custom sound effect. However, depending on your typing speed and the performance of your system, the sound effect may not be in sync with the actual key press.
One of the few advantages the Celluon device has over I-Tech is the mouse feature. By pressing a special mouse key, the entire board acts like a mouse pad, allowing you to move your mouse just by moving a finger around the projection area. Pressing the mouse key again toggles the device back into keyboard mode.
The basic problem with both devices is that they're geared more towards small mobile devices like cell phones and PDAs, where the only competition are mini-keyboards where the user typically doesn't require all the normal PC keyboard functionality.
Furthermore, a problem with the Celluon Laserkey is that they seemed to have spent most of their effort on marketing and product display, and less on making a useful, functioning keyboard. The look and feel of the Celluon device oozes quality, but the actual features fall short in comparison to the I-Tech.