Pioneering research has discovered how smart devices talk to Android apps and each other to share data that allows them to know who enters a home, when, and how much they earn
Security risk is the bigger concern IMHO. These devices are often a security weak point for networks. Putting them on their own wifi network and then isolating that network is critical.
How can you ensure this is done? There are so many devices that need to connect to the internet and some that require access to other network devices to function.
You basically need to employ network engineering level security - very tight firewall rules, use NAT where it's available (IPv6 removes NAT, which ipv6 apologists will tell you is a good thing - they're wrong, as it removes per-service level control and moves it out to per-device/per-NIC), and punch very specific holes to grant access where needed.