Designing a vault whose front door is a working calculator

Why Lock It: Calculator Vault hides a private, AES-256 encrypted vault behind a calculator that does real math.

Lock It: Calculator Vault

17. Oktober 2026October 17, 2026 · 2 Min. Lesezeit2 min read

Phones get passed around all day: to show a photo, share directions, or let someone make a quick call. That's normal. But most of us also keep a few things on our phones that are nobody else's business, and a home-screen icon labeled "Vault" invites exactly the question you'd rather not answer.

That was the starting point for Lock It: Calculator Vault, our Android app. Here are the design choices behind it.

The front door has to be a real calculator#

The calculator can't be a prop. It does real math and behaves like any other calculator app, so someone borrowing the phone can use it and never see anything unusual.

The vault opens only when you type the equation you chose and press =. There's no separate unlock button and no hint on screen.

Lock It calculator screen

What lives inside#

Once you're in, the vault holds the things people actually worry about:

Lock It private vault screen

Security you can see#

We wanted the security story to be visible, not buried in a FAQ. The app's security screen explains the AES-256 encryption used for vault contents.

Lock It AES-256 security screen
Lock It private messages screen

What it costs#

Lock It is free with ads. Premium Pro is $4.99/month, and Offline Vault is a $9.99 one-time purchase.

Try it#

Search "Lock It: Calculator Vault" on Google Play, or use this link: Lock It: Calculator Vault on Google Play

Disclosure: this article comes from the team behind Lock It: Calculator Vault. It was written with AI assistance and reviewed before publishing.

#android#apps#privacy

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Contents

5 sections

  1. The front door has to be a real calculator
  2. What lives inside
  3. Security you can see
  4. What it costs
  5. Try it