Rhodamine B (Rh-B) an available dye has been developed as novel and efficient colorimetric and fluorometric chemosensor for cyanide ions in an absolutely aqueous media. The UV-vis absorption and fluorescent emission titrations experiments have been employed to study the sensing process. RhB could act as an efficient "ON-OFF" fluorescent response for phosphotungstic acid (H3PW12O40 or PTA) based on an ion associate process. Also (Rh-B(+))(3)center dot PTA(3-) could operate as an "OFF-ON" fluorescent sensor for cyanide anions based on a ligand substitution process. It has been identified as highly sensitive probe for CN- which responds at 0.3 and 0.04 mu mol L-1 concentration levels by absorption and fluorescent method respectively. Depending upon the sequence of addition of PTA and CN- ions into the solution, RhB could be as a molecular security keypad lock with PTA and CN- inputs. The ionic inputs to new fluorophore have been mimicked as a superimposed electronic molecular keypad lock. The results were compared successfully (>96%) with the data of a spectrophotometry approved method (EPA 9014-1) for cyanide ions. (C) 2013 Elsevier B.V. All rights reserved.