From what I understand, there's no internet connection, thus no app.
But, since you mentioned, my two cents on the app-only baby monitors: parents want to be sure they can tend to their little ones as fast as possible. Before buying the monitor we choose, I researched a lot of options and read tons of reviews. The app-only monitors do have the advantage of one less device and being able to watch from anywhere, but they come with a huge disadvantage: latency. I even got to test a device who had both a parent unit and could send the images to the internet to be viewed from an app or even in a browser. The latency on that particular model was over one second, when the internet connection was optimal. And that's considering you have the app/browser already on all the time. One second might not look like much, but it's plenty of time for a hungry baby to go from sad-hungry to crazy-mad-hungry. But that's not all. If you rely on the notifications, no matter how much you fine-tune the sensibility on the sensors, there was over 15 seconds of delay between the event and the notification. If a lot can happen in one second, imagine 15 and over. I guess having to pass through multiple servers across the globe until coming back to appear on your phone is fine for Facebook notifications, but not for a crying baby. If you leave your phone on the app the whole time - you would have to keep touching the screen to prevent it from closing automatically - your phone battery would discharge pretty fast. I guess we don't want that, either.
In the parent unit there was also latency, but of a few milliseconds tops, and it did not varied since it was a direct connection. And the sound is always on - the screen turned off after some time to save battery - so we could be sure to listen to any calls as soon as they happened.
And that's not to mention the security issues. So far, from what I read, there's no perfect solution. There will always be vulnerability. And while the chances of one particular unit getting hacked are low - unless you are some celebrity - I particularly don't want to take that risk.