The U.S. Air Force is the latest organization to get stung by one of the uglier secrets of the chemical defense business. That is, chemical detectors dont work very well, and often dont work at all. The concept of a portable instrument, that could detect the presence of chemical weapons, and that was rugged enough so that combat troops could take into a combat zone, works in theory. It even works in the laboratory. It doesnt work that well in practice. In early 2003, the air force bought a hundred handheld ChemSentry detectors, at $10,000 each, for use by air force troops in Afghanistan and Iraq. Subsequent tests revealed that the ChemSentry gave a high number of false positives and often misidentified the chemical agent it had detected, or thought it had detected. The manufacturer, BAE, has been trying to perfect a military version of the ChemSentry for seven years now. The ones the air force bought were civilian models. 

The problem with chemical detectors is that, to work, they must detect chemical weapons before the concentration is high enough to kill or incapacitate people. In most cases, troops will encounter clouds of chemical weapons, or the stuff will be on the ground and vegetation, and small concentrations will be encountered first. This is what chemical detectors are supposed to detect. The problem is, making a rugged, reliable, and especially portable (hand held) chemical detector has, so far, proven, well, impossible. The ChemSentry is just another failure in a long line of attempts.

Current efforts, and there are several, to create a workable ChemSentry type device began after the 1991 Gulf War, when it was discovered that even the bulkier, vehicle mounted, detectors, didnt do so well. But 13 years later, everyone is still trying. And will continue to keep trying.