Many home cameras today send video the the cloud to, for example, analyze the difference between a leaf blowing in the wind or someone at your door.
Apple aims to improve this with a new feature called HomeKit Secure Video with on-device analyzing. An encrypted stream is then sent to iCloud that no one, not even Apple, can see. You'll be alerted to activity and can review what's going on.
HomeKit is also coming to routers, effectively adding a firewall between smart home accessories and your network. Launch partners will include Linksys, Eero, and Charter/Spectrum.