What makes a private diary app private

Almost every diary app calls itself private. It’s on the store page, in the title, sometimes in the icon. But “private” can mean very different things, and the difference only matters on the night you write something you really don’t want read.

So instead of taking the word on trust, here are five questions to ask any private diary app — and how Diary BFF answers each one.

1. Who can open it on an unlocked phone?

This is the question most people mean when they say “private”. Your phone already has a passcode. The trouble is that the people most likely to read your diary — a partner, a parent, a roommate — often know it, or are holding your phone with it already unlocked.

If a diary app opens because the phone is unlocked, it’s only as private as your phone.

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 checks whether this is the phone’s owner, and a phone gets unlocked for plenty of people who aren’t the person writing the diary. Someone can be holding your unlocked phone and still not open your diary.

2. What shows up on the lock screen?

A reminder that quotes your last entry is a small leak on a screen anyone can glance at. Notifications from Diary BFF never include what you wrote, because they can appear on a lock screen.

3. Is your writing used to train AI?

Diary BFF has an AI in it — your diary BFF, who replies when you ask. That makes this question more important, not less. Your entries are not used to train AI. And the replies aren’t written by a person.

It’s worth checking this one in any app with AI features: look for the sentence in the privacy policy, not the marketing page.

4. Can you get your writing out?

A private diary you can’t leave isn’t fully yours. In Diary BFF you can export your diary any time — every entry, with your writing, the timestamps and the replies — and the backup file can have its own lock.

5. What happens when you delete something?

Deleting an entry should be a decision, not an accident. In Diary BFF, deleted entries wait 30 days in Recently Deleted, where you can restore them, and then they’re gone.

What the privacy is for

Privacy in a diary isn’t a feature for its own sake. It’s what lets you finish the sentence.

Diary BFF is built for the end of the day, when you’re lying in bed and your head won’t stop. You open it and you’re on tonight’s page — no sign-up, nothing to set up first. You write whatever is going round. When you want, 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, and on Sundays it writes you a letter about your week.

Your writing, the chat and the replies stay together on one page for that night, behind its own PIN.

A short checklist

Before you write in any private diary app, ask:

Does it have a lock of its own, separate from the phone?
Do notifications stay quiet about what you wrote?
Does the privacy policy say your writing isn’t used to train AI?
Can you export your entries whenever you like?
Is there a way to undo a delete — and a point where deleted means deleted?

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.