A new multisignaling sensor based on rhodamine B with a ferrocene substituent (1) has been synthesized and has been shown to display extreme selectivity for Hg2+ over other metal ions. Multisignaling changes are observed through UV/vis absorption, fluorescence emission, and electrochemical measurements. Furthermore, by means of confocal laser scanning microscopy experiments, it is demonstrated that 1 can be used as a fluorescent probe for monitoring Hg2+ in living cells.