If you regularly make phone calls from noisy places, the Aliph Jawbone headset is a must-have accessory. The Jawbone uses military-inspired technology to remove background noise from your side of the conversation, sampling the background 500 times per second and continually adjusting its filters for the sounds it encounters. Noise-canceling microphones are nothing new, but the Jawbone's adaptive techniques give it an edge over passive systems and those that simply subtract the sound from two opposed microphones.

The unit consists of two sections: an earpiece/microphone with a behind-the-ear loop and a control unit that clips onto your belt or lapel. The earpiece measures 0.8 by 2.1 inches and weighs less than an ounce. It has a rubbery button on the back that rests against your cheek; contact with your face helps the unit determine which sounds you are making and which are in the environment. The control unit is 0.9 by 2.1 inches. Both have sleek, brushed stainless-steel skins over translucent white plastic. The control unit has a defeat switch to turn off the noise canceling (so you can use it as a regular headset) and a button that can mute, answer, or end calls, depending on the phone you're using.

We tested the Jawbone in a variety of conditions, including standing next to a diesel-powered commuter train as it pulled out of the station. We tested it in a raucous club, on a city street, and in our listening room, with seven speakers and a kilowatt of amplification buffeting us. In each situation, our party could hear us clearly, even when conditions were occasionally so loud that we couldn't even hear ourselves—or them. The Jawbone automatically increases the earpiece volume to try to compensate for loud conditions, but obviously in some instances it's a losing battle.

In the listening room, we used test tones, sound-effects recordings, and a sound-level meter to quantify the Jawbone's efficacy. We recorded the other end of the phone call on a PC so we could analyze its actions. We found the Jawbone extremely effective against broad-spectrum sound, such as roaring traffic, airplanes, and crowd noise. It quickly counteracts siren noises, squelching them after a few tenths of a second, but they occasionally break through when they cross into human speech frequencies. We played test tones at 95dB to 100dB (very loud for continuous tones) and tried to speak in a normal voice. Although we couldn't hear ourselves, the Jawbone relayed our words properly, with very slight breakup or background leakage at the beginning of each phrase. (There was no chance of hearing our party at that level, however.)

The Jawbone is larger and more expensive than most headsets, but it is uniquely effective in blocking out background noise. Since it uses active electronics, Aliph estimates that it can reduce battery life by 15 to 25 percent, but you can switch off the active component when you don't need noise reduction. The Jawbone currently works only on certain Ericsson, Motorola, and Nokia phones, but more are in the works, as is a wireless version.