Move a file between two devices in the same room.

Two lanes of sixteen tones, 17.0 to 18.6 kHz, 25 bytes a second. Nothing to pair; the other seat only has to be in earshot.

1. Pick a band. Quiet is the default.
2. Start listening, and allow the microphone.
3. Watch the waterfall for stepping tones.
4. Ping, to check the other device.

Everyone in earshot hears this. To talk, go to Comms.

What this device can work out about the room it is in, from physics alone. Nothing is sent anywhere and nothing is kept.

A browser cannot be calibrated, so some of these are relative rather than absolute. Each reading says which it is: measured is a real quantity, relative has no reference to compare against, and assumed rests on a stated constant.

A birdseye map of what actually reaches this spot, measured while you walk. Position comes from counting steps and a compass, so the map stretches and drifts; walk back to where you started and say so, and it corrects itself.

1. Stand still. Press Start walking.
2. Walk the space at a steady pace.
3. Return to the start and close the loop.
4. Read where the channel holds up.

Two phones, one clock, no network. A chirp there and back measures how far apart their clocks are; a few of them measure how fast the two are drifting away from each other.

1. Link the two devices first.
2. Open this page on both.
3. Press Sync. They chirp at each other.
4. Fire together, and film the proof.

Every device chirps in turn and the others answer, each in its own slot. One chirp gives one device its distance to everyone in earshot, and the distances draw the room.

1. Link the devices, then open this page on each.
2. Press Start on all of them.
3. Watch the map fill in as they hear each other.

Not started.

Distances fix the shape and nothing else. Where the room is, which way it faces, and whether it is the right way round are all unknowable from sound alone - a room and its mirror image measure identically - so this device is drawn at the centre and Flip swaps the handedness.

Most of fyzx rests on a speaker that can make 18 to 21 kHz and a microphone that can hear it. Plenty of phones cannot do either. This chirps at itself and tells you what will work here, before you take two devices into a room and find out the slow way.

Reach is estimated, not measured: sound pressure falls as one over distance, the speaker and microphone are about 10 cm apart, and the detector gives up at four to one. It ignores the room, which helps, and it is taken on the device's best axis, which flatters it. Treat it as an order of magnitude - the difference between "not at all" and "across a room" is a hundredfold, and nothing subtler matters.

A chirp says how far away the nearest wall is. The compass says which way you were facing. Your steps say where you were standing. Put the three together from a few spots and the room draws itself.

1. Stand still. Press Sweep here.
2. Turn slowly, all the way round.
3. Walk a few steps. Sweep again.

Not started.

The beam is 60 degrees wide, so one sweep from one spot draws arcs rather than walls: a return says something is three metres away somewhere in a wide cone. Sweeping from a second spot looks straight through the first spot's arcs and rubs out everything that was not really there. Metre-scale honest, centimetre-scale fiction, and it reaches seven metres.

The screen only shows ciphertext. A photograph of it gives nothing.

1. Pick a passphrase both devices know.
2. Add a message, or attach a file.
3. Seal and send, or seal and save.
4. They type the same passphrase.

Nothing sealed.

The passphrase above, made visible: the keystream, and the picture with that keystream subtracted from it. A demonstration only, and it goes one way. To send a picture somebody can open, use Scatter.

Nothing split.

Sealed arrivals land here.

A picture out as noise, and a way back. The phrase is minted here, eighty bits. Send it separately from the picture.

1. Choose a picture; it leaves as noise.
2. Save the picture, copy the phrase.
3. Send the two by different routes.
4. They gather it with the phrase.

Send the file, never a photo of it. A re-encode or a resize destroys it, and the app says so rather than hand back noise. What comes back is a dither, which is all three bits a pixel can hold.

Each batch asks: re-encode, or send the original. To send text, use Comms.

1. Add photos from this device.
2. Choose re-encoded, or the original.
3. Point their camera at this screen.
4. Broadcast, for more than one camera.

Watching

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Confirmed

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1. Pick the chain and paste an address.
2. Add an amount, if you want one.
3. They scan the code, or copy the URI.

1. Paste the unsigned PSBT or transaction.
2. Check the inputs, outputs and fee.
3. Send to the signer, or show UR.
4. The signed one comes back the same way.

Kind

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Inputs

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Outputs

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Sending

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Fee

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