Starting today, millions of Comcast customers can activate a free feature on their Xfinity routers that uses Wi-Fi motion sensing. This technology alerts users to movements in the home through the Xfinity Internet app, offering a cheap alternative to traditional security systems.

The update arrives as part of the new Xfinity Shield service and requires an advanced gateway, such as XB7 or newer. Users can enable Home Watch, Away Watch, or Dark Watch modes based on their needs. While Comcast sees it as adequate for average households, it’s not meant to replace camera-based security yet.

Comcast has spent three years refining the algorithms behind Wi-Fi motion sensing. Although some companies like Linksys and Wiz have experimented with similar technologies, none have scaled them quite like Comcast is doing now. The potential applications range from home security to monitoring vulnerable individuals as they age in place.

Kohposh Kuda, SVP of consumer products at Xfinity, told The Verge that WiFi Motion pairs well with other services such as Xfinity Shield Select, which offers security cameras and door/window sensors for a monthly fee. This dual approach allows Comcast to maintain a robust suite of home security options while introducing this new, cost-effective feature.

As the technology gains traction, it'll be interesting to see how far it can go in safeguarding homes without breaking the bank.