A passive infrared (IR) sensor of chemical weapon agents (CWA) is being developed using a new approach (patent pending) for differential absorption radiometry (DAR). The sensor can be packaged as a handheld device, unattended sensor, remote imager and more. An agent is detected by its IR absorption (or emission) viewed through a bandpass filter centered at one of its strong spectral lines. A second detector is equipped with a filter centered at a frequency that was optimized to provide near perfect correction for background absorption by at least one atmospheric species, e.g., water vapor. The net absorption by the CWA is obtained by subtracting the reference signal of the background detector from that of the CWA-dedicated detector and normalized by dividing it by the total signal. A simple electronic circuit provides normalized differences to within 1:106. This new approach replaces spectral scanning wiht detection at strong pre-selected spectral bands of chosen species and provides near perfect correction of absorption by pre-selected background species. The DAR is more efficient and thus more sensitive than alternative passive remote sensors. Specificity can be enhanced by integrating multiple DARs into a a single system using detector-filter arrays.