I am personally using an expensive Nest IQ cam (cost around 300 USD) and some cheap IP camera in parallel with this AiCam app. For me the physical security camera are good to install outside my house or where I do not care if the video footage may be leaked or hacked.

But I have some use cases which I did not find any security camera suited for it, it also the reason why I developed this app:

- I want to monitor my sleeping room, but I trust no security camera brands.

- I want to integrate the camera into my home automation system and use event like person, animal detected to trigger some workflows.

- I want to detect more complex events like unfamiliar faces, fire, baby crying and not just simple motion or sound to avoid false alarms. This is the main point why a phone is more suitable, because most smartphones have required compute power to do all the AI work offline.

- Also a mobile phone have some additional advantages like you mentioned (integrated battery as UPS), cellular network as a backup to send alert when power or internet is down.

All in all it depends on what features are you expected from a security camera.