There are many keychain flashlights out there, but none are as impressive and useful as the Acebeam UC15. This is a keychain flashlight for people who want a powerful light and don't mind the trade-off; this is slightly bigger than other keychain lights (but still smaller than most EDC flashlights in general). It's about the same size as the keychain fob that I use to unlock my car.
You don't have to use it as a keychain light. It works great as a "pocket rocket", a small light that lives in your pocket and has disproportionally more power than its size would make you think. You can install the included clip if you want to attach it to a cap (to use like a headlamp), or a belt or pocket for quick access.
I love that it has a red LED, a UV LED, and a standard white LED. It's easy to switch between the colors, and these LEDs make the light useful in a variety of situations. Just for fun, turn on the UV and look at the doorknobs in your house - it reveals that you need to clean them! There is room for improvement in the color LED group. Just like the white LED, the color LEDs should have low-mid-high to make them more useful and help with runtime. Currently the only way to change the brightness of red/UV is to change batteries: 10440 Li-ion is brighter, AAA NiMH is dimmer. With 10440 Li-ion, red is so bright that it doesn't preserve night vision, which is what many people might use it for, but it's more usable for that purpose with AAA NiMH.
Speaking of batteries, another thing that makes the UC15 stand out among keychain flashlights is the ability to use two 10440 Li-ion batteries, or two AAA. Get some button-top 10440 batteries for more lumens (Acebeam sells 10440s, as do many other online retailers) or use AAA batteries (I recommend eneloop) for longer runtime with less lumens. The UC15 also works when only one battery is inserted. Having easily replaceable batteries makes the UC15 so much better than other keychain lights, for several reasons: (1) You can bring extra batteries if you expect to need more runtime. (2) The ability to work with one battery or buy a battery at a nearby store could be useful in an emergency situation. (2) As battery technology advances you can easily "upgrade" your UC15 with better batteries. (3) A typical keychain light is basically trash because they usually have a built-in battery that wears out after 3 years, and the only option is usually to dispose of the light in the garbage. Don't buy trash. Buy the UC15! When your 10440 batteries wear out (in 3 to 10 years, depending on usage), you can just buy more batteries and keep using your UC15!
The user interface is good. As you might expect for a light with multiple LED colors, it may take a few minutes to learn for the first time. It memorizes your last used mode (only red or UV or white are memorized; it does not memorize moonlight or turbo). It has a lockout, which is toggled by holding the button for 5 seconds. I appreciate the mode memory and lockout features.
Hopefully the successor to the UC15 will have brightness options added for each LED color. And a high-CRI white LED for even more utility and enjoyment. And a moonlight mode that is less bright, like 1 lumen or less (or just have a moonlight group and memorize the last used option in the group). And, if possible, a slightly slimmer and more waterproof design. Even without those suggested improvements, the Acebeam UC15 is the best keychain flashlight available today!