The electrochemical behavior of the pyrrole-substituted crown ether ferrocene 1 was investigated in detail in 0.1 A I TBAP + CH3CN by cyclic voltammetry (CV) and chronoamperometry. In the potential range 0-0.7 V, a reversible diffusion-controlled process was observed with a formal potential of 0.53 V corresponding to the ferrocene/ferricinium redox couple. Electro-oxidative polymerization of 1 was accomplished either by repeated CV scans, or by controlled potential electrolysis. The resulting polymer films were tested in acetonitrile electrolyte for the amperometric recognition of alkali and alkaline earth metal cations. Their remarkable recognition properties towards Ca2+ and Ba2+ cations have been confirmed by electrochemical impedance spectroscopy (FIS). EIS allowed construction of a calibration curve based on the variation of the low frequency capacity of the film as a function of the guest cation concentration, reflecting the variation of the formal potential between the free and the complexed immobilized redox couple. Capacity measurements using EIS appear to be an attractive method for cation sensing with films based on molecular redox receptors.