Novel integrated N ‐(2‐pyridyl)pyrazole‐hemicyanine dyes (PH) were synthesized as promisor chemodosimeters for colorimetric and ratiometric CN – detection. These dyes, obtained by a three‐step sequence starting from acetophenones in up to 69 % overall yield, are donor–π–acceptor (D–π–A) systems consisting of indolium‐salts bearing a modular donor aryl group on its pyrazole ring PHa–e . The salts displayed high selectivity and sensitivity for CN – (LOD of up to 9.9 × 10 –7 m ), as determined by interrupting the modular D–π–A system by nucleophilic attack of the cyanide on its iminium group; the mechanism of this process was confirmed by Job′s plot experiment, spectral analysis, cyclic voltammetry studies and TD‐DFT calculations. This probe changes its color from deep yellow to colorless and can be used for in‐the‐field measurements without special equipment, since this change can be easily observed by the naked eye; indeed, yellow test strips were suitably used to detect CN – in water.