Data privacy is probably not on your mind when you log a feed at 3 a.m. Still, a baby tracker can hold a detailed picture of your family's routine, so it is worth knowing what the app collects and where that information goes.
Start with the App Store privacy label
The App Privacy section shows what an app collects, whether that data is linked to your identity, and whether it may be used to track you across other companies' apps and websites. You can check the label before downloading anything, which makes it a useful first step when comparing baby trackers.
Why an account matters
If an app asks you to create an account, your records are usually stored somewhere beyond your phone so they can sync back to you. That is not automatically a problem, but you should be able to find out where the data is stored, who can access it, and what happens when you delete your account.
How Nerumi handles your data
Nerumi does not require an account and does not store your records on its own servers. The app contains no third-party analytics or advertising tools. Your entries stay on your device and, if you turn on iCloud, sync through your own iCloud account. You can confirm this in Nerumi's App Store privacy label.