<p>Continuous and spatially distributed data of snow mass (snow water equivalent, SWE) from automatic ground-based measurements are increasingly required for climate change studies and for hydrological applications (snow hydrological model improvement and data assimilation). We present and compare four new-generation non-invasive sensors that are based on electromagnetic waves for direct measurements of SWE: Cosmic Ray Neutron Probe (CNRP); Gamma Ray Monitoring (GMON) scintillator; frequency-modulated continuous-wave radar (FMCW-Radar) at 24 GHz; and Global Navigation Satellite System (GNSS) receivers for SWE retrieval. All four techniques are relatively low cost, have low power requirements, provide continuous and autonomous measurements, and can be installed in remote areas. Their operating principles are briefly summarized before examples of comparative measurements are provided. A performance review comparing their advantages, drawbacks and accuracies is discussed. Overall instrument accuracy is estimated to range between 9 and 15 %.</p>