URL: https://diarybff.app/diary-with-pin/ Date: 2026-10-28 Author: Daniel Chen, founder of Diary BFF Published by Diary BFF

Diary with PIN — its own code, not your phone’s

A diary with PIN protection sounds like an obvious idea. Most phones already have a passcode, so why would a diary need another one?

Because the people most likely to read your diary are usually the people who already know your phone passcode. A partner who unlocks your phone to pick a song. A parent who set it up for you. A roommate who has watched you type it a few hundred times. To your phone, all of them look like you.

Diary BFF opens with a PIN of its own. It isn’t your phone’s passcode, and it isn’t Face ID. Your phone can be unlocked, sitting on the couch next to someone else, and your diary still asks for its own code.

How the PIN works

You set a PIN the first time you open the app. There is no sign-up — you write, and the PIN is the lock.

After that, the app asks for the PIN when you open it. Your phone’s passcode doesn’t open it. Your face doesn’t open it either: Diary BFF has no Face ID or Touch ID unlock, by design. A face unlock answers “is this the phone’s owner?”, and a phone gets unlocked for plenty of people who are not the person writing the diary.

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

Picking a good diary PIN

A diary with a PIN is only as private as the PIN you pick. Three things help:

Don’t reuse your phone passcode. That’s the most common mistake, and it undoes the whole point.
Don’t use a date someone close to you would guess — your birthday, an anniversary, the year you graduated.
Pick something you’ll still remember at 2am. You’ll mostly be opening this diary late at night, half asleep. A PIN you have to look up isn’t a lock, it’s a note.

If you forget your PIN

Because you never made an account, there is no password-reset link to send. Here’s what happens instead.

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 while you wait.

Ten days is a long time when you want to write tonight, and that’s deliberate. A reset you could finish in a minute with the phone’s passcode would be a back door for exactly the people the PIN is there for.

The details around the PIN

A PIN on the front door doesn’t help if the windows are open. A few other parts of Diary BFF follow the same idea:

Notifications never show what you wrote. Notifications can appear on a lock screen, so they don’t carry your words.
Your entries are not used to train AI.
Exports can have their own lock. You can export your diary whenever you like, 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 PIN is protecting

Behind the PIN is a night diary with someone in it.

You write whatever your head is doing — the conversation you keep replaying, the message you didn’t send, tomorrow’s list that keeps rewriting itself. 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 earlier nights and tells you which night it means.

On Sundays, it writes you a letter about your week. Your writing, the chat and the replies all stay on one page for that night, the way a diary should read.

Who a diary with a PIN 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 alone to open.
Anyone who has stopped halfway through a sentence because of who might read it.

If that’s you, the PIN is the feature, not the friction.

Getting started

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.