Why everything stays on your device

When you write something in Underweather — a temperature, a rough night, what you've taken — it's saved on your device. Not in an account. Not on a server of ours.

A health diary is about as personal as a record gets. The safest place for it isn't a database somewhere that you have to trust; it's the device already in your pocket. So we built Underweather the other way around from most apps: your records stay with you by default, and that's the whole arrangement.

In practice, that means a few simple things. There's no sign-up to keep your notes. It works without a connection. And there's nothing of yours sitting on our side to be lost, leaked, or pored over — because we don't hold it in the first place.

The safest place for a health diary is the one already in your pocket.

It's worth being honest about the other side of that. Because your records live on your device, they're yours to look after. If you move to a new phone, or lose one without a backup, the notes can go with it. Keeping a backup is the one small habit worth having.

When you're keeping track for more than one person — a child, a partner, a parent — each of them is kept on the same device, side by side, and all of it stays just as private.

There is something old-fashioned in that, and we mean it kindly. A diary has always been a private thing — kept in a drawer, not handed around. Underweather treats your notes the same way: yours to keep, yours to read back, and no one else's to see.

Underweather can also offer a short daily reading: a few plain sentences that put your day into words. It's the one feature that reaches beyond your device — when you ask for it, that day's details go to an AI service (Anthropic's) to write the response, and they're never used to train its models. It's optional, it's disclosed plainly, and like the rest of the app it reflects your day back to you — it doesn't diagnose, and it never tells you what to take.

The short version: your record is yours. We built Underweather so that keeping it private took no effort on your part — it's simply how the app works.