American telecommunications and media company Comcast has turned millions of modern Xfinity router devices into home motion sensors. The WiFi Motion feature can detect movement between the router and fixed wireless devices without a camera or separate sensor, then send an alert to the Xfinity app within the new Xfinity Shield home protection platform.

According to a report published by BleepingComputer, a US-based cybersecurity website, the WiFi Shield feature is free for customers using compatible devices. It combines malware and phishing protection with family settings and motion monitoring. Comcast offers the Shield Select package for $15 per month, which includes an internal camera, door/window sensor, cloud storage, and 24/7 emergency response.

The body changes the Wi-Fi signal path

Users select fixed devices such as a smart speaker or thermostat. When a body moves in the space between them and the router, it changes the reflection and scattering of WiFi waves. The software analyzes this disturbance and concludes that there is movement. Xfinity says the feature does not identify the person or their exact location. It is optional and disabled by default, but it may mistake a small child for a pet of the same size.

Home data raises privacy question

Comcast documents state that information resulting from WiFi Motion can be shared with third parties without additional notification in law enforcement investigations or disputes in which the company is a party, or to comply with a court order or subpoena. At the same time, the company says it does not monitor movement or alerts. However, the documents do not specify what kind of data is retained, how long it is stored, or what can be delivered when a legal request arrives. This makes the router both a security tool and a new source for highly sensitive data at the same time.