Two new reaction-based molecular probes ResCo and ResCu are reported for the selective colourimetric and fluorometric detection of Co²⁺ and Cu⁺, respectively. The receptor in these probes differs by a single metal coordinating site combined with resorufin as a common reporter dye, which exhibit visible absorption and emission in the longer wavelength regions. Co²⁺- and Cu⁺-mediated oxidative benzylic ether (C–O) bond cleavage in ResCo and ResCu, respectively, releases resorufin dye which offer ‘switch-on’ fluorometric and ratiometric visible absorption (colourimetric) in a reducing aqueous environment. Reaction-based selective detection of Co²⁺ and Cu⁺ is demonstrated in the presence of all other competing metal ions. Submicromolar concentration of Co²⁺ and Cu⁺ can be easily detected through dual signaling (fluorometric and colourimetric) pathways. The probes ResCo and ResCu are employed for ‘switch-on’ fluorescence live cell imaging of Co²⁺ and Cu⁺, respectively, in HEK293T cells.