A new bimetallic complex, (CN)₃Feᴵᴵ(tppz)CuᴵᴵCl (tppz = 2,3,5,6-tetra(2ʹ-pyridyl)pyrazine) including an Fe(ıı)-diimine indicator and a dual functional Cu(ıı) receptor/catalyst, was synthesized to demonstrate the concept of indicator/catalyst displacement assay for the simultaneous detection and detoxification of cyanide. The catalytic degradation property in the assay was necessary for making the detecting system reversible, which the traditional indicator displacement assays could never achieve. After the realization of this new property, silica-gel-based solid-supporting complex 1 was fabricated for application in a device, which was demonstrated for its use in the naked-eye detection and degradation of cyanide in tap, river, and underground water samples in a repeatable and real-time manner, even in the presence of interfering anions (CH₃COO⁻, N₃⁻, HCO₃⁻, Cl⁻, NO₃⁻, HPO₄²⁻, SO₄²⁻, SCN⁻, and OCN⁻). Within 300 min, cyanide was quantitatively oxidized into the less toxic cyanate by 1 in the presence of H₂O₂. The detection limit of 1 for cyanide was found to be 1.16 × 10⁻⁴ M (3.02 mg L⁻¹). Copyright © 2020 The Royal Society of Chemistry.