Secret Contacts: Locked Book

Two address books: the one anybody can open, and this one. Four digits or a glance to get in, and the entries stay encrypted on the phone itself.

Two address books are better than one.

The contacts app that came with your phone is fine for most of the people in your life. This one is for the rest of them. It opens with a code only you know, and shows nothing at all until it does.

Setting it up takes about ten seconds Choose four digits the first time you launch the app. They have nothing to do with the code on your Lock Screen, and neither one will open the other. After that it is four taps — or a glance, once you switch Face ID on.

An entry can hold A name. A phone number. An email address. And a memo line, which is where most of the useful part tends to end up: how you met, which of the numbers is the work one, what was said last time, what you still owe.

It shuts itself There is no lock button to remember and no timer to configure. Swipe up, take a call, check a message — by the time you come back it is asking for the code again.

Where the numbers actually sit Inside this phone, in a file AES-GCM has already scrambled, with the key held in the device keychain. Nothing is uploaded, because there is nowhere to upload it to: the app has no account system and never asks for an email address. Switch the network off completely and it behaves exactly the same.

One warning. Uninstalling the app takes the entries with it, permanently, and nobody — the developer included — can bring them back. Write your four digits down somewhere safe.

Ads cover the cost of the app. A single in-app purchase turns them off for good.