Short Description:

[UPDATE Dec, '04] - Newer models of the O4 appear to no longer have the constant-on switch. They are momentary operation only. Do not expect to have a constant-on lever on any O4 you purchase now.

The CMG "o4" is a single LED keychain light produced by CMG Equipment. The "o4" consists of a single white LED in a plastic and rubber body. The light reviewed has a clear plastic body. The body of the light comes in various colors.

It has a momentary-on push button and a lever which swings over and presses the momentary-on switch, taking the place of your finger and keeping the light on constantly.

The rubberized parts of the body allow for an easy grip and allow the light to be held comfortably between the teeth for hands-free lighting. The entire body is sealed against the environment by a rubber gasket.

The "o4" uses two 2016 lithium coin cells which provide 6 volts. The batteries are replaceable by removing the screw on the back of the light and opening the case in clamshell fashion. CMG has placed a threaded brass insert in the body of the light to receive the screw in order to prevent stripping and increase durability.

Internally the LED is attached to a thin membrane contact that wraps around the 2 batteries. When open, the membrane flops out of the way allowing for the battery change. A screwdriver and some sort of tool to pry apart the 2 halves of the body are required for a battery change.

o4 vs. Photon 2 - size comparison

Reviewer's Impressions:

The CMG "o4" is a good compliment to any camping kit or activity which requires the use of a close range personal light. The fact that this little light is truly watertight is an added bonus for a keychain sized light.

The "o4" is a little larger than some of the other keychain lights reviewed in the past, but still small enough to remain relatively unobtrusive in the pocket.

The momentary-on switch is very sensitive and requires surprisingly little pressure to turn on. This could cause the light to turn on in your pocket or pack, so it would be wise to pack it in such a way that the chances of this are minimized.

The constant-on lever, although appearing to be an unconventional solution, does work very well. When received it did not keep the light on constantly, but a slight tightening of the screw that holds the lever in place (as directed by the included instructions) fixed the problem. There is a probability that the lever could get caught on things, as it protrudes from the side of the body of the light.

The shape of the light, with the larger "head" opposite the split ring attachment area makes this light very handy as a zipper-pull for a jacket. The lithium batteries are impervious to cold, and the light is watertight, so it would make a good addition to a winter jacket zipper. Plus you'll always have the light with you.

The LED only comes in white, but the plastic surrounding the LED comes in various colors. The colored translucent plastic bodied lights I have seen light up a little bit when the LED is turned on, allowing the light to serve as a marker to some degree.

+ + + Pluses: Durable, Watertight, Constant-on switch, Can be held in mouth comfortably

- - - Minuses: Lever may catch on things, LED exposed to potential damage, case requires tools to open, could come on accidentally if pressed against something in pocket/pack