That would require Comcast to have access to your router, or more precisely, the NAT.
Comcast sells a router gateway combination device that's probably required for this motion sensing anyway. If you have that they could already check device counts and in fact their Xfinity app lists connected devices in detail.
For most people their Comcast modem _is_ their router.
Comcast sells a router gateway combination device that's probably required for this motion sensing anyway. If you have that they could already check device counts and in fact their Xfinity app lists connected devices in detail.