Code Buddy

Pick a word — your dog’s name, your favourite band, something daft — and tell one friend and nobody else. Type a message and watch it turn into little symbols: stars, squares, moons, circles. To anyone who doesn’t know your word it’s gibberish.

The good bit is that none of it needs a network. Instead of sending the symbols, the phone can blink the message out loud — the screen, the torch, beeps, buzzes, or all four at once — and your friend watches from the other side of a dark room and taps along as it arrives.

• The Grid tab shows what your word actually did: it shuffles the alphabet into a five by five square, and every letter becomes a row and a column
• Once you’ve seen that, you can do the whole thing on paper without the app
• Build symbol packs of your own and send them to a friend as a link
• Hard mode shifts every letter as the message goes, so the same letter never looks the same twice

It’s a puzzle, not a lock — the sort of code a patient person cracks with a pencil and an afternoon, which is exactly what makes it as fun to break as it is to write. Nothing you write leaves the phone.