We propose a coupling-induced intensity-sensing mechanism based on a microring resonator. Different from the conventional intensity sensor, the resonator is working under the analyte-induced variable coupling. The coupling coefficients are highly sensitive to changes of the analyte, thus leading to significant analyte-dependent output intensity. This advanced sensing mechanism is proved with a detection limit of $1.23\times {10}^{-7}$ , predicted based on the coupled-mode theory. By introducing a phase bias in the Mach–Zehnder interferometer, the detection limit may be enhanced further to $4\times {10}^{-8}$ , which is demonstrated to be up to 1 order of magnitude more sensitive than that provided by comparable conventional sensors.