NullKey 
Lock screens and storage are different
Before you trust a secure notes app on Android, check where the notes are actually stored, whether an account or sync is involved, how recovery works, and what your keyboard, clipboard and exports can expose. A lock screen on the app is not the same as encrypted storage. The lock decides who can open the app, while the storage format decides what a copied file looks like to anyone else.
An app can show a sign-in or PIN screen and still keep notes in plain files that could be copied through a device backup or a sync service. Ask the developer what is stored, in what form, and whether the stored form depends on a key that stays on your phone.
Accounts and sync change the picture
An account means a server may hold something about you, even when the notes themselves are scrambled. Check whether sign-up asks for an email address, whether notes are sent to a server, and what the provider can read or reset. An app that keeps everything on the phone and needs no login narrows the number of places a copy can end up.
Sync is useful when you change phones, but it also copies mistakes. Many sync services apply a deletion everywhere at once, so a note you remove on one device can vanish from the others.
Recovery decides what you can lose
Ask what happens if you forget your passphrase or PIN. Some apps offer an account reset, so check whether that also restores access to encrypted notes. Others may offer no reset at all, so the route back may be a recovery secret you saved earlier, another unlock method that is still enabled, or a backup. Neither design is automatically better, but you should know which one you have before you put real notes in it.
Recovery is not the same as backup. A recovery secret can unlock a vault that still exists, but it cannot rebuild notes lost with the phone. Check whether the app can make a backup you can store away from the device, and whether you can practise restoring it before you need it.
Keyboard, clipboard and exports
Every keystroke goes through the keyboard you are using. On many phones a third-party keyboard can see text typed into any field, depending on its permissions and settings. Accessibility services can also read what is on screen. A notes app cannot switch these off, so ask whether the app adds exposure of its own.
Copying text is the next leak. Many phones keep a clipboard history, and other apps may read whatever was copied. Look for whether the app marks copied text as sensitive, whether it clears its own clipboard entry, and whether it says plainly that copies held by other apps stay where they are.
Exports are the last check. A readable export is a plain copy of a note or file. Once it is written to a folder or a cloud provider, the app's protection no longer covers that copy, so find out whether exports work item by item or for the whole vault, and where the file would go.
A short checklist before you commit
Run these steps with dummy notes before you move anything real.
- Write a test note with harmless text, lock the app and confirm the lock works.
- Check whether sign-up asks for an email address and whether sync is switched on.
- Save the recovery secret somewhere separate from the phone, then confirm you can find it.
- Type into the note, copy a line and check what the clipboard holds afterwards.
- Export one test item, see where the file lands and delete that copy afterwards.
- Make a backup, restore it into an empty place and open a few notes.
How NullKey handles this
NullKey keeps notes, photos and documents in an encrypted vault on your phone, with no account and no ads. NullKey asks Android for no internet permission and has no developer server behind it. Alvento never receives your vault contents, passphrase, recovery key or decryption keys, so nobody can reset a lost secret for you.
The limits are real. While a vault is unlocked, readable content is processed in memory, and a compromised phone or keyboard can still see what you type. NullKey has no keyboard of its own. It attempts to clear its own clipboard entry when Android permits, and other apps may keep copies. Readable exports leave the vault's protection, file sizes are not hidden, and there is no automatic backup.
