A diary lock for the moments your phone isn’t only yours

Most of the time your phone is yours. A diary lock is for the other moments: when it’s in someone else’s hands for a minute, or sitting unlocked on the table while you’re in the other room.

Diary BFF has a diary lock of its own: a PIN that’s separate from your phone’s passcode. Here’s what that means in the moments that matter.

When you hand someone your phone

You pass your phone to a friend to show a photo. Someone borrows it for a game. Your phone is unlocked, and for a minute, everything on it is reachable.

Your diary isn’t. Someone who picks up your phone while it’s unlocked can’t open your diary without the PIN.

When someone knows your passcode

Plenty of people share a phone passcode with a partner or family. That’s fine for the phone. It shouldn’t be fine for a diary.

Someone with your phone passcode can’t open your diary. And Diary BFF doesn’t offer Face ID or Touch ID unlock, by design, so there’s no shortcut around the PIN.

When your phone lights up

A diary lock isn’t much use if your words show up on the lock screen. Notifications never show what you wrote, because they can appear on a lock screen.

When you forget the key

If you forget your PIN, you can start a reset with your phone’s own device authentication. For your privacy, the new PIN only unlocks after a 10-day wait, so someone who knows your phone passcode can’t use it to open your diary today. Your entries stay intact.

What’s behind the lock

A night diary that can write back. You write what’s on your mind; when you ask, your diary BFF answers in a few sentences, right under your words. The replies aren’t written by a person; your diary BFF is an AI that lives in your diary. It remembers what you wrote, with the date.

Your entries are not used to train AI. You can export your diary any time, and the exported backup can have its own lock.

Who it’s for

People whose phone gets passed around.
People who share a passcode, but not a diary.
Anyone who wants to write honestly and know it stays shut.

Try it tonight

Download Diary BFF, set a PIN, and write one entry tonight. Your first reply comes with the app; more replies and the full Sunday letter are part of the full version.