Current methods for the detection of tear gas residues require extensive sample preparation before spectral measurement. This contrasts with the work reported in this paper in which a new detection method for the active ingredients of CN, CS, and pepper sprays (capsaicin and crude pepper extracts) has been developed, based on ambient temperature, atmospheric pressure ion mobility spectrometry. The minimum determinable limits were 0.1 mg for CN, 25 mg for CS, and 5 mg for cayenne pepper. These limits were dependent on the vapor pressure, proton affinity, and electronegativity of the target molecule. The study concludes that ion mobility spectrometry can be used to detect the vapors produced at ambient temperature by traces of CN, CS, and cayenne pepper. The findings suggest that for complete coverage of the most commonly encountered lachrymators, sample preheating must be used. The ability to obtain spectra in both modes sequentially adds an extra dimension to compound identification. By analyzing first in the negative ion mode and then in the positive mode, it is possible to discriminate between these and other compounds. The results indicate that with further method development, this instrumentation will be of value in the rapid screening of scene- of-crime samples and suspect spray cans for these compounds. 8 figures and 12 references