It would work even better. From the linked support page:

"Motion is detected based on the amount of signal disruption taking place between the Xfinity Gateway and your selected WiFi-connected devices, so motion from small pets (around 40 pounds or less) can be filtered out while keeping you notified of large movements more likely to be caused by humans."

With enough signals, gait recognition for example is possible, and those same signals could be corroborated with presence or absence of concomitant device signals to determine if your device is moving with your person, and if not, to then flag this for enhanced monitoring if evasion is suspected.