  We propose a new sensing method based on the measurement of the second-order
autocorrelation of the output of micro- and nanolasers with intensity feedback.
The sensing function is implemented through the feedback-induced threshold
shift, whose photon statistics is controlled by the feedback level in a
characteristic way for different laser sizes. The specific response offers
performances which can be adapted to different kinds of sensors. We propose the
implementation of two schemes capable of providing a quantitative sensing
signal and covering a broad range of feedback levels: one is utilizing the
evolution of g$^{(2)}$(0), the other one is the ratio between central and side
peaks in g$^{(2)}(\tau)$. Laser-threshold-based sensing could, thanks to its
potential sensitivity, gain relevance in biomolecular diagnostics and security
monitoring.
