A wireless multi-range, mass velocity sensor assembly for remote monitoring with direct on-site visual validation of mass velocity is provided. In certain implementations, the sensor assembly comprises a channel body fixture, an obstruction mounted within an aperture formed in the inlet or outlet of the channel body fixture, and an arcuate indicator that protrudes above the fluid flow path and provides clear visual readout of the flow velocity. In some implementations, the sensor assembly can be easily adapted for existing back check valve and other back flow prevention devices.