Can our phones hear each other?

A test for the ephemeral network, run in a real room. It plays and listens for tones from 2 kHz up to 21 kHz, most of them too high for adults to hear, and measures what actually gets through. Nothing leaves this phone except the numbers you choose to send: no names, no recordings, no location. Children may hear the highest tones, and dogs and cats will: keep it short around them.

1 · this device

press start

2 · one phone plays

On the phone that plays: press play. It steps through 2, 17, 18, 19, 20 and 21 kHz, each for 1.2 s, at the same loudness, and repeats. Set the volume to about half.

3 · another phone listens

On the phone that listens, about 1 m away: listen with the browser's cleaning off for 12 s, then again with it on. Each bar is how far that tone rose above the room's own noise.

not yet

4 · how far does 19 kHz carry?

The playing phone holds 19 kHz. The listening phone watches the number below while you walk apart. Type the distance in metres and press mark at a few places, and at the point where it drops below 10 dB.

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5 · send the numbers

This is exactly what will be sent. Add a word about the device if you like (for example "iPhone 15, Safari").

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