Broadcast a second wifi network that blocks all outgoing traffic(i.e. no ability to access the internet or devices on the rest of your network). Use any ONVIF network camera with wifi (hikvision or dahua make good cheap cameras), put them on that locked down wifi, and configure your network so that your NVR can reach the cameras.
Ideally, you would use wired PoE cameras (and either fully air gap that network or separate it like my WiFi recommendation), but if you’ve gotta go with WiFi, pick one that’s designed for use with an on-prem nvr and not a cloud service.
Why do they need fo be open source?
Broadcast a second wifi network that blocks all outgoing traffic(i.e. no ability to access the internet or devices on the rest of your network). Use any ONVIF network camera with wifi (hikvision or dahua make good cheap cameras), put them on that locked down wifi, and configure your network so that your NVR can reach the cameras.
Ideally, you would use wired PoE cameras (and either fully air gap that network or separate it like my WiFi recommendation), but if you’ve gotta go with WiFi, pick one that’s designed for use with an on-prem nvr and not a cloud service.