Send a Message by Sound
Play a message as tones and let another device hear it — no network at all.
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About the Send a Message by Sound converter
Two devices in the same room can talk to each other without sharing a network, a Bluetooth pairing, or an account. One plays a sequence of tones; the other listens through its microphone and reads them back as text.
It is the answer to a specific and annoying moment: getting a link from a laptop to a phone when the Wi-Fi is behind a login page, when the machines are on different networks, or when one of them has no network at all.
How a message becomes a sound
The text is turned into a sequence of eight tones spaced between 1000 and 2400 hertz, each held for a fraction of a second. Eight tones carry three bits apiece, so a short message takes a few seconds to play.
That frequency range is chosen deliberately. It sits comfortably within what every phone speaker can produce and every laptop microphone can pick up — higher tones would be less intrusive but far less reliable on ordinary hardware. The transmission is audible, and sounds a little like a fax machine, which is roughly what it is.
A marker tone opens and closes the transmission, the length is sent before the message, and a checksum follows it. If the checksum does not match what arrived, the page says the message may be damaged rather than presenting a corrupted result as though it were correct.
Where this is genuinely useful
Captive-portal Wi-Fi in hotels and airports is the obvious one: your laptop is online, your phone is stuck at a login screen, and there is no easy way to move a link between them. Sound does not care.
It works between devices on different networks, between a machine with no network at all and a phone, and across an air gap where connecting the two would be a policy violation. It also works when the only thing you have in common is being in the same room.
It is audible, and it is not private
Anyone within earshot hears the transmission, and anyone with this page can decode it. This is passing a note across a room, not sealing an envelope.
If the contents matter, encrypt them first and send the result — the tones carry whatever you give them, so an encrypted string travels exactly as well as a plain one.
Frequently asked questions
Does this need internet?
No, and that is the point. Nothing is sent over any network at any stage. The sending device makes a noise and the receiving device listens to it — both work with the network off entirely.
How much can I send?
A few hundred characters. It is meant for a link, a code, a Wi-Fi password or a short note. Sound is a slow channel, so a long message would take minutes and be far more likely to be interrupted.
Why can I hear it?
Because audible tones are far more reliable than ultrasonic ones. Above roughly 18 kilohertz, cheap speakers stop producing usable sound and many microphones stop recording it, so an inaudible version would fail on most hardware.
Is the microphone recording me?
No. The audio is examined frame by frame for tone frequencies and discarded immediately — nothing is stored, and nothing is sent anywhere. The microphone is released the moment you stop listening.
The message came through garbled.
Move the devices closer together, raise the volume, and reduce background noise. Music and conversation in the same frequency range are the usual culprits. The checksum tells you when the result cannot be trusted, so you know to send it again.
Is it secure?
Not at all, and it does not pretend to be. Everyone in the room can hear it. Encrypt anything sensitive before sending it, or use a method that was designed for secrecy.