Human skin gas is the term used to describe gas emanating from the human skin surface. Ammonia, one such gas, has a pungent odor affecting body odor. As ammonia's dermal emission increases with physical load and/or psychological stress, the resulting body odor is called “fatigue odor.” Previously, human skin gases were collected via direct contact or headspace sampling, using a homemade sampling probe or bag and passive flux sampler. We developed a wristband-type wearable device for rapid, on-site detection of dermal ammonia based on headspace passive sampling coupled with Alizarin red as a pH indicator. Color change was measured with a colorimetric indicator tested in an exposure chamber and calibrated using dermal emission flux measured with a passive flux sampler. The indicator was developed as a tablet-like device comprising a polyethylene terephthalate body with a transparent window, detection sheet, diffuser, and disk with concentric spaces. The detection sheet was prepared by pipetting 50 μL 0.1 % Alizarin red–1 % glycerol into a methanol solution onto a cellulose filter paper and drying. The colorimetric indicator was placed on the skin surface using a wristband. For quantitative evaluation, the color-change amount was evaluated using color difference (ΔE*ab), which was calculated from L*, a*, and b* measured using a spectrophotometer. The colorimetric response to ammonia on the colorimetric indicator was evaluated by comparison with the conventional passive flux sampler. Good correlations were obtained between the color change amounts and those collected with the passive flux sampler. To simulate living human-skin conditions, the influence of temperature and humidity was also tested, and the effect on the passive indicator was clarified. Compared to conventional dermal ammonia-measuring methods, this newly developed passive indicator was more user-friendly because the results were obtained on-site without external evaluation. The passive indicator was also found to be an effective and simplified instrument for dermal ammonia measurements.