A free Wi‑Fi upgrade taps existing gateways and stationary devices to map in‑home movement with signal shifts. Your modem's Wi-Fi can be used as a security tool. Key points and original sources are listed below.

• A free Wi‑Fi upgrade taps existing gateways and stationary devices to map in‑home movement with signal shifts.S1

• Your modem's Wi-Fi can be used as a security tool.S2

• Comcast is promoting WiFi-based motion detection as a part of its new Xfinity Shield home protection platform, allowing routers and wireless devices to detect people moving through a home without cameras or motion sensors.S3