 Non-interferometric tests in opto-mechanical systems. In 2003, an interesting proposal of testing the superposition of a mesoscopic mirror was put forward (Marshall et al. 2003). This stimulating proposal faced strong technical difficulties, such as environmental decoherence, which prevents the detection of the superposition. There is, however, a side effect of collapse theories that can be exploited in such systems. Indeed, the collapse of the wavefunction leads to an effective noise on the center of mass of the system (Collett &amp; Pearle 2003), which can be eventually bounded through experiments. The optomechanical application has been proposed (Bahrami, Paternostro, et al. 2014; Nimmrichter, et al. 2014; Diosi 2015) to test such an effect, and various experiments showed the potential of this technique. They range from nanomechanical cantilever cooled to millikelvin temperature (Vinante, Bahrami, et al. 2016; Vinante, Mezzena, et al. 2017) to the gravitational wave detectors LIGO, AURIGA and LISA Pathfinder (Carlesso, Bassi, et al. 2016; Helou et al. 2017) as well as optically or magnetically levitated systems at room temperature (Zheng et al.  2020; Pontin et al. 2019 [Other Internet Resources]). Recently, several proposals were presented to push even further the bounds on the collapse parameters, which now place constrains just below f = 10−8 sec−1 at d = 10−7 m. These proposals exploit different possible modification of current experiments, for example a multi-layer structure of the test mass (Carlesso, Vinante, et al. 2018) would amplify the bound for particular values of d. One can also consider different degrees of freedom, for example the rotational ones could in principle be more sensitive to collapse effects (Carlesso, Paternostro, et al. 2018; Schrinski, Stickler, &amp; Hornberger 2017).  A first application was implemented in a torsional experiment (Komori et al. 2020). 