Perhaps the most notable feature of the K800 is the updated illumination feature that now can be turned on and off using the power switch on the top right of the board. Additionally, you can now dial in the amount of illumination using the secondary function key in conjunction with the F5 and F6 button. It brightens and dims in three increments: low, medium, and high visibility. Finally, the keyboard also includes a built-in sensor that automatically fades out the backlight and can detect your hands as they approach and turn it off as you move your hands away from the device. All of these features are incorporated to conserve precious battery life, as this is the first illuminated keyboard from Logitech to include rechargeable AA nickel metal hydride (NiMH) batteries.
You can also use standard AA alkaline batteries if you're in a pinch, but the Micro-USB cable and port on the top of the keyboard make it easy to recharge using a simple computer connection, and Logitech rates the battery life for up to 10 days on a single charge.
Like many of Logitech's peripherals, the K800 is part of the Unifying receiver family that lets you connect a single USB plug to six compatible mice and keyboard devices. Each one comes with its own Unifying receiver, meaning that you can conceivably leave them all plugged into several different computers at home and at work. Keep in mind that buying into the Unifying connection means locking yourself into Logitech products only, but we can't ding Logitech since the Unifying design also frees up USB ports previously occupied by other devices.
Our only critique of the K800 is the fragility of the keyboard's chassis. We've tested plenty of Logitech keyboards in the past that felt solid and unbreakable, but the K800 allows for a significant amount of flex, so much so that we're wary of its long-term durability. We assume that the wafer-thin profile has a lot to do with it, but the amount of bend allowed by the keyboard is suspect nonetheless.