An apparatus for detecting exposure to at least one hazardous substance is provided. The apparatus includes a body having a plurality of openings, and an attachment mechanism coupled to the body. Each opening is sized to receive a cassette for detecting the presence or absence of at least one hazardous substance. The cassette can include a colorimetric sensor having a base layer fabricated from a hydrophobic film, a colorimetric coating for covering the hydrophobic film, and at least one hydrophobic membrane for controlling the exposure of the specific substance to the colorimetric coating.