New Delhi, July 22 -- At home, most people think of Wi-Fi only as a tool for internet access. Modern routers, though, are much more than that. Many can now follow movements inside your house. This is real technology, not science fiction. The signals moving between your router and devices can detect when you stand, walk, sit, or even breathe. Indian homes are seeing these smart features more often as brands bring new devices to market.

A Wi-Fi router sends out signals to your devices. When you move, these signals bend and scatter. Even a small shift on the sofa or a person walking to the kitchen changes the way signals travel. The router collects data about these changes. Special software reads the patterns. Without cameras or microphones...