When you say "app" do you mean something that will let you view remotely through a residential NAT connection with no port forwarding or hole punching? Because 99.9% of those options are inherently not private.
If you only need the camera itself to have a local feed i.e. you already have some kind of VPN/tunnel/etc. into your home network, then something like a cheap Amcrest works fine and does not require Internet access for the camera itself.