The article presents a multiband passive sensing system that senses the environment by reusing Wi-Fi signals that are already being transmitted, in line with the IEEE 802.11bf standardization work. By combining channel state information from the sub-7 GHz and millimeter-wave bands, it makes single-band passive sensing more accurate and reliable at detecting human presence, movement and activities indoors. Using a new model called MilaGro, the system performs robustly in scenarios such as monitoring presence in workspaces and tracking movement along corridors, and the experiments show the gain obtained by integrating multiband data. The work also addresses the main security concerns raised by passive sensing and proposes measures to mitigate them, advancing low-cost, non-intrusive monitoring that depends less on active sensing infrastructure.