Settings
Both devices must use the same frequencies and speed. Give each device a different channel to let them talk at the same time, and a different device number.
What the mic hears
Live spectrum, 0–22 kHz, newest at the top. Shaded strips are the two channels; the brighter one is yours.
Send a message
Up to 48 bytes (about 48 English characters).
Messages
Everything this device sent or decoded. Green = received from the other device. Grey = this device hearing itself. Red = a message claiming to be from you that you didn't send.
Test bursts: measure how well it works
The sender plays a burst of numbered test packets. The receiver already knows what each packet should contain, so it can count exactly how many arrived intact. Add a label on the receiving device (for example "2 m, cabin, quiet") to keep a record.
| Time | Label (edit) | From | Settings | Received | Signal quality | Speed |
|---|---|---|---|---|---|---|
| No bursts received yet. Press "Send test burst" on the other device. | ||||||
Replay attack demo
This device keeps a recording of the last message it decoded. Playing it back makes the other device believe it was sent again. Sound has no built-in security; this shows why anything important needs a check such as a PIN.
Experiment checklist
- Hello: send a text from the laptop, read it on the phone, then the other way round.
- Distance: test bursts at 0.5 m, 1 m, 2 m, 4 m, and through a closed door.
- Speed: repeat at each speed until delivery drops.
- Near-silent: switch both to Near-silent (17–20 kHz). Can you hear it? Does it still work?
- Both at once: laptop on Channel 1, phone on Channel 2, both press Send together.
- Noise: play music or talk nearby during a burst.
- Replay: send from the laptop, then replay it from the phone.