SideAppComparison · 7 min read · · Checked
Private Diary App for Android: Lock vs Encryption
A diary with a code is not always encrypted. What a lock, encryption on the phone and end-to-end encrypted sync protect, and which diary app fits which need.
A diary app with a code stops someone from opening it; an encrypted diary keeps the pages unreadable without the key, even if the app's files are copied. A private diary needs both, and one more answer: are your pages kept on the phone, or on someone's server? What follows explains the difference, then compares three diary apps from their own documentation, checked on 6 November 2026.
In Short
- A code or fingerprint lock decides who can open the app. On its own, it says nothing about how the pages are stored.
- Encryption on the phone makes the stored pages unreadable without the key, for example if the app's storage is copied.
- End-to-end encrypted sync matters only if your diary goes to a server: the pages are encrypted before they leave the phone, and the provider cannot read them.
- No app can protect a diary on a phone that is already compromised (rooted and infected) while the app is unlocked.
- MemoLock locks the whole diary behind a code or your fingerprint and encrypts it on the phone. It has no sync: the pages stay on the phone you write them on.
Three Kinds of Protection
| Situation | Code or fingerprint lock | Encryption on the phone | End-to-end encrypted sync |
|---|---|---|---|
| Someone picks up your unlocked phone | Protected | Not on its own | Not on its own |
| The app's storage is copied | Not on its own | Protected | Only the server copy |
| The provider's servers are breached | No server copy | No server copy | Protected |
| Malware runs while the diary is open | Not protected | Not protected | Not protected |
A lock is the part you see. Encryption is the part you have to take on trust, so look for an app that says plainly what it encrypts and where the key is kept. Our guide to password-protected notes goes further into the same distinction.
On the Phone, or Online?
A diary website or a diary app with an account keeps a copy of your pages on its servers. That has real advantages: the same diary on your phone and your computer, and nothing lost if the phone is. It also means your diary is only as private as that service's encryption and your password for it.
A diary kept only on the phone has the opposite trade-off. Nothing to breach elsewhere, but no copy elsewhere either: you need a backup you make yourself, and you can't read your diary on another device.
Paper has the same trade-off, minus the lock and the search. If you are choosing between a paper diary and an app, the question is less "which is safer" than "who could open it, and what would they find".
Three Diary Apps, From Their Own Documentation
| App | Where it runs | Lock | Encryption | Sync |
|---|---|---|---|---|
| MemoLock | Android 7.0 and later | Code (number pad or with letters) or fingerprint, for the whole app | On the phone: the diary with SQLCipher (AES-256), photos and voice notes with AES-256-GCM | None: no account, no Internet permission |
| Day One | iOS, Mac, Android, Windows and the web, free to download on iOS, Mac and Android | On Android: a 4-digit passcode or a fingerprint, for the whole app | End-to-end encryption with Day One Sync, in the free plan too | Free plan: cloud backup from one active device; sync between devices in the paid Silver and Gold plans |
| Journal (Apple) | iPhone, iPad and Mac | Face ID, Touch ID or your passcode | Journal data in iCloud is end-to-end encrypted | Through iCloud, between your Apple devices |
Sources: Day One plans and features, Day One end-to-end encryption FAQ, Day One passcode on Android, Apple: iCloud data security overview, Apple: protect your journal entries on iPhone.
Two details from those pages are worth knowing. Day One says that if you lose your encryption key, a journal stored in Day One Sync can't be decrypted, and that its text backups and JSON exports are not encrypted. Apple says end-to-end encrypted data can be decrypted only on your trusted devices, and that Journal entries are not included in iCloud backups, but sync with iCloud when Journal is turned on in iCloud settings.
When to Pick Something Else
MemoLock is built for one phone, on purpose. Pick another app if:
- You use an iPhone: MemoLock is Android only. Apple's Journal locks with Face ID and keeps its iCloud data end-to-end encrypted.
- You want the same diary on several devices or on a computer: MemoLock has no sync. Day One syncs between iOS, Mac and Android with end-to-end encryption, in its paid plans.
- You want to write in a browser: MemoLock has no web version. Day One has one: its journal can be opened from any browser.
What MemoLock Does
MemoLock 2.6 turned the app into a diary, with your notes kept in a second tab:
- One page a day, or several, and you can write for yesterday: an entry's day can be changed, and the calendar lets you write on any past day.
- The month's calendar shows the mood of each day you wrote.
- "One year ago" and "one month ago" bring back what you wrote on that day.
- A question of the day at the top of your diary, all day, from 30 questions in the app's language; hide the ones you don't like and add your own. Here are the 30 questions.
- Writing streaks and moods of the last 30 days, computed on the phone from your entries.
- Locked behind a code or your fingerprint, again as soon as you leave the app, with an increasing wait after 3 wrong codes (up to 1 hour). Screenshots and the recent-apps preview are blocked by default.
- Encrypted on the phone, with a random key protected by the Android Keystore. The key is not derived from your code: the code controls who opens the app.
- Backup: the whole vault, diary included, in one file encrypted with a password you choose, to restore on a new phone.
MemoLock is free, with no account and no ads, and it does not have Android's Internet permission. Its privacy policy lists what it stores and every permission it asks for.
Frequently Asked Questions
Is a diary app with a password encrypted?
Not necessarily. The password or code stops people from opening the app; encryption is a separate feature. Check the app's privacy policy or documentation for what it encrypts and where the key is kept. MemoLock does both.
Can someone read my diary if my phone is stolen?
With MemoLock, they need your code or your fingerprint to open the app, and the stored diary is encrypted. As with any app, nothing can protect a diary on a phone that is compromised (for example rooted and infected) while the app is unlocked.
What if I forget my MemoLock code?
If you set up a secret question in Settings › Security, it lets you choose a new code. Without a recovery method, a forgotten code can't be recovered: nobody else holds a copy of the key.
Does MemoLock back up my diary to the cloud?
No. MemoLock stays out of Google backup and has no account. You make an encrypted backup file yourself, in Settings › Backup, and keep it where you want.
