This PubMed-listed review examines how 5G deployment (denser small cells and beamforming) changes RF-EMF exposure patterns and evaluates the validity of low-cost sensors for 5G exposure monitoring. Reviewing over 60 studies across Sub-6 GHz and emerging mmWave systems, it reports that well-calibrated low-cost sensors can approach professional instruments within a few dB, but highlights persistent challenges such as calibration drift, frequency coverage gaps, and data interoperability. The authors argue that standardized calibration protocols and open data frameworks could help low-cost sensors complement professional monitoring and improve transparency.