) in this REAL system is measured as a function of the laser power. A noise model considering the respective noises (see Methods for SNR analysis of REAL) was used to fit the experimentally measured total noise. The close-to-linear relationship between the noise power and the laser power is an indication that the shot noise indeed dominates. With this noise model, a fixed amplitude vibration (11.6 mm) from a mask excited at 500 Hz by a loudspeaker (Figure 2d) is used to examine the signal model, i.e. vibration modulated intensity change, and hence the signal to noise ratio. The experimental SNRs detected at different distances are plotted in Figure 2f and our proposed SNR model could well fit the experimental data based on the theory of spherical wave propagation (see Methods for SNR analysis of REAL). Additionally, based on the proposed model, a few other parameter configurations (laser power and vibration amplitude) are calculated in Figure 2f as a guide to help design similar systems. If we set SNR = 0 dB as the detection limit, our current configuration would allow a remote detection range of 17 meters.