Colorimetric detectors indicate the presence of a target through a chemical or biological reaction that results in a color change. Results are typically examined by comparison of the resulting color to a key in the test kit. However, a few vendors offer electronic readers that provide more objective results than visual comparison and can store the results of a test. Detection limits are typically in the part-per-million to part-per-thousand range (ppm-ppth), depending on the target, with some radiological targets dipping into the part-per-billion (ppb) range.
Typically colorimetric detection has a small form factor and can be easily transported by hand. As the tests are based on chemical or biological reactions, they generally require little or no additional power to conduct. There are a small number of radiological colorimetric test kits available. Kit cost varies depending on the target and the number of reagent packets in the kit. They typically require one-time use consumables such as cartridges, reagents, papers or swabs for each target.