Calculator Vault

The problem with vault apps

Every app that promises to hide your files announces itself on the home screen. A shield icon, a padlock, a name with "vault" or "hide" in it — the moment someone scrolls your apps, they know there is something to look for. The lock is the advertisement.

That is the flaw we wanted to remove. Not a stronger lock, but no visible lock at all. The app had to be genuinely secure — real encryption, real isolation from the rest of the device — while looking like the most boring thing on the phone.

Two layers, doing different jobs

Calculator Vault protects content twice, and the two layers are deliberately independent.

The first layer is what people notice: the app is a working scientific calculator. Not a facade with a fake keypad — it computes, it has history, it is the app you would reach for if you actually needed a calculator. There is no login screen, no "unlock" button, and nothing in the launcher that suggests a second purpose. The vault opens by typing a secret PIN on the calculator keypad, the way you would type any other sum.

The second layer is the one that matters if someone gets past the first. Files imported into the vault are moved into app-private storage — a directory Android isolates from other applications, from system file managers and media scanners, and from Auto Backup and Google One. The entry PIN is hashed through Jetpack DataStore and never written in plain text, so reading the raw storage yields nothing usable.

Obscurity alone is not security, which is why the second layer exists. But obscurity is what keeps the first conversation from happening at all.

Building it

The app is Kotlin and Jetpack Compose end to end, structured with clean architecture: eighteen single-responsibility use cases, strict separation between the UI, domain and data layers, Hilt for dependency injection, and type-safe Jetpack Navigation between screens.

That structure is not ceremony. A vault app has an unusual number of ways to leak — a thumbnail cached in the wrong place, a file handed to a system share sheet, a media scanner indexing a directory it should not see. Keeping every file operation behind a named use case meant each of those paths had exactly one implementation to audit, rather than being scattered across view models.

Room handles vault metadata, DataStore handles the hashed PIN and preferences, and nothing at any layer opens a socket. The app requests no network permission at all, which makes "your files never leave the device" a property the operating system enforces rather than a promise in a privacy policy.

What it feels like to use

The parts users touch got the same attention as the parts they do not.

Photos, videos and files each get their own vault with date-grouped grids, a full-screen viewer, multi-select bulk actions, and search that filters as you type. Files takes PDFs, documents and archives, not only media. A Tools tab adds a password generator and encrypted notes, on the reasoning that the things people write down are usually the things they most wanted hidden.

Settings is where the product's honesty shows. It states plainly that files are encrypted on the device, offers to export the entire vault back to the gallery in one action, and offers to clear it — warning first, because with nothing stored off-device there is no recovery. Loading states are shimmer skeletons rather than spinners, transitions are animated, feedback is haptic, and layouts adapt properly to landscape.

The result is an app that behaves like a well-made Material 3 product in every respect except one: from the home screen, there is nothing to find.

Where it stands

Calculator Vault is live on Google Play, published and maintained by Aquison Technologies. It collects nothing, transmits nothing, and requires no account to use — claims the privacy policy sets out in full, and which the absence of a network permission makes verifiable rather than merely stated.