This paper reports a robust sensing method using nonlinear micromechanical resonators for applications such as resonant mass and thermal radiation sensors. Resonators show stochastic response by applying noise, in which resonators show two vibration states, i.e. large vibration amplitude state and small vibration amplitude state. Single resonator acts as a bistable element, and from responses of the parallel array, the response can be averaged and the total noise can be decreased. We have designed and fabricated such piezoelectric resonator array with ability of self-sensing and self-actuation, and demonstrated noise-activated detection of heat from light. This kind of noise-activated system can be highly robust against external noise and have potential applications to various sensors operated in noisy conditions.