A secret diary app, like the one with the tiny key

A lot of people had one: a small diary with a gold clasp and a key you hid somewhere clever. The lock was flimsy. It didn’t matter. What made it a secret diary wasn’t the strength of the lock — it was that the diary had a lock of its own, separate from everything else in the house.

A secret diary app should work the same way. Diary BFF is built around that idea.

The key: a PIN that isn’t your phone’s

On a phone, everything opens with the same key: your passcode. The trouble is that a passcode is a shared thing. A partner knows it. A parent set it up. A sibling watched you type it a hundred times.

So a secret diary app needs a key of its own. Diary BFF opens with its own PIN, separate from your phone’s passcode. There’s no Face ID or Touch ID shortcut, on purpose — a face unlock only checks that the phone is yours, and phones get handed around. Someone can be holding your unlocked phone and still not open your diary.

If you change the PIN later, the app asks for the current one first.

The hiding place: nothing on the lock screen

The paper diary only stayed secret if it stayed out of sight. On a phone, the place things leak is the lock screen. Notifications from Diary BFF never show what you wrote, because they can appear on a lock screen.

The pages: only yours

A secret diary is the place you write what you wouldn’t say out loud. A few things in Diary BFF follow from that:

Your entries are not used to train AI.
Exports can have their own lock. You can export your diary any time, and the backup file can be locked too.
Deleted entries wait 30 days in Recently Deleted, where you can restore them, and then they’re gone.

What the paper diary couldn’t do

A paper diary listens perfectly and never says anything back. Diary BFF is a secret diary with someone in it.

You write whatever is on your mind. When you ask, your diary BFF reads it and says one thing back: a few sentences, at most one question, no lists and no lectures. It remembers what you wrote, with the date, so when something comes up again, it can tell you which night it was. On Sundays, your diary BFF writes you a letter about your week.

And it stays quiet when you don’t ask. A secret diary shouldn’t interrupt you.

If you lose the key

A paper diary’s key could go missing down the back of a drawer. A PIN can be forgotten too. Because there’s no sign-up, there’s no password-reset link to send. Instead, you can start a reset with your phone’s own device authentication, and 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 while you wait.

Who a secret diary app is for

People who share a phone passcode with a partner or family.
People who live with others and want one place on the phone that’s theirs to open.
Anyone who has stopped mid-sentence because of who might read it.

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.