Keeping them in Mupi

This is the middle option: the phone is still a phone, but while a child is holding it there is nothing on it except Mupi. It takes about a minute to set up, two taps to start, and it undoes itself completely.

Turn it on once

1. Open Settings, then Accessibility.
2. Scroll to Guided Access and turn it on.
3. Open Passcode Settings and set a Guided Access passcode. Use one your child does not know — not the phone's own passcode, which they will watch you type. Face ID or Touch ID can end a session too, and is the easier way to get back in.
4. Still in Guided Access, turn on Side Button. This is the setting worth knowing about: with it on, pressing the side button sleeps the phone the way it does normally, so a child can put the camera down and it goes dark. Without it, the screen stays on until the battery is gone.
5. Turn on Volume Buttons as well if you want them left alone, or off if you would rather a child could not change anything.

Every time you hand the camera over

1. Open Mupi.
2. Press the side button three times quickly. On a phone with a home button, press that three times instead.
3. Tap Start, top right.

To stop

Triple-press again and use Face ID or Touch ID, or enter the Guided Access passcode and tap End.

What Mupi does differently while it is on

Mupi can tell when the phone is held inside it, and behaves differently when it is. None of this needs configuring — it is what being locked in means.

• The camera goes to sleep. After 45 seconds of nobody touching anything, Mupi stops the viewfinder and shows a faint camera instead. Any touch anywhere brings it straight back. On an ordinary phone it does not do this, because there the phone's own auto-lock already handles it — but a phone that can never leave Mupi has no auto-lock to fall back on, and a viewfinder nobody is looking at is the fastest way to flatten a ten year old battery.
• FaceTime disappears. If you have given a grown-up a FaceTime number, the camera offers to call them — but not while the phone is held inside Mupi, because iOS does not let an app open another one and Mupi cannot change that. The option to take a photo and send it to them stays, and that one works with no signal at all.
• The way to the family library gets harder to hit by accident. The hold on the camera header goes from one and a half seconds to three. It is still a hold rather than a puzzle: what actually keeps a child out is your device passcode, which Mupi asks for either way.

Worth knowing

• Guided Access is Apple's, not Mupi's. Mupi can notice it and cannot start, stop, or configure it — including the side button, which iOS gives no app any say over.
• It has to be started again after the phone restarts. That is the main reason families with a permanently repurposed phone prefer a dedicated camera.
• A child who watches you triple-press and type the passcode can let themselves out. Use Face ID, or a passcode you do not use in front of them.