WiFi signals penetrate walls and enable through-wall detection of motion, coarse interior mapping, and in advanced cases, human pose or breathing estimation — without cameras or line-of-sight.
Key patents include:
• US9696421B2 (2017, SRC Inc.): Handheld monostatic WiFi/cellular radar system. Transmits at 2.4 GHz (or cellular bands), analyzes reflected signal entropy/variance to detect human activity perturbations behind walls. Supports portable devices and networked multi-unit coordination for localization.
• US9185528B2 (granted 2015; app. US20140004874A1, Northrop Grumman): Multi-transceiver setup using RSSI and tomographic backprojection for structure mapping plus motion detection via EM field disturbances from moving bodies. Incorporates building construction priors; designed for COTS WiFi hardware in urban/first-responder scenarios.
MIT’s 2013 Wi-Vi demonstrated low-power WiFi reflections tracking people through walls. Later CSI AI work (e.g., Carnegie Mellon) has reconstructed body poses/shapes. Commercial routers and smart devices now ship basic WiFi sensing for presence/motion.