The nonemissive iridium complex 2 is a lab-on-a-molecule for the highly selective detection of Hg2+ and ClO- among 33 analytes using its oxime residues as reactive units. At pH 5, chemodosimeter 2 responds to Hg2+ by dehydration, whereas at pH 8, it is oxidized by ClO-, resulting in 450- and 235-fold emission increases, respectively, at two distinct wavelengths.