Tondavo (formerly chirpfile) is a web app for moving files and text between two nearby devices. It encrypts a file in your browser, uploads only the encrypted copy, and sends the key to the other device as a short sound. Below are 123 answers about Tondavo and about moving files between devices in general. Where another tool does the job better, we say so.
Updated 27 September 2026
The one rule to know: messages of 120 characters or less travel only as sound and are not encrypted, so anyone nearby with a decoder could read them. Files and longer messages are encrypted in your browser, and only their key travels as sound.
Tondavo is a web app that moves files and text between two nearby devices. The browser encrypts the file, uploads only the encrypted copy to a relay, and plays the decryption key from the speaker as a short sound. The receiving device hears the key through its microphone, downloads the file and decrypts it.
It needs no account and no install, and the two devices don't have to be on the same network. Tondavo was called chirpfile until September 2026, and the app still runs at chirpfile.com while the move finishes.
Yes. Tondavo is the new name for chirpfile, from September 2026. Nothing about how it works has changed: same app, same encryption, same limits and prices. The app still runs at chirpfile.com while the move finishes, so some pages and the app itself still say chirpfile. Links to chirpfile.com keep working.
A Tondavo transfer takes five steps:
Short messages of up to 120 characters skip the upload entirely: the message itself is the chirp, and it is not encrypted.
No. You don't need to install anything to use Tondavo: it runs in the browser on both devices. If you use it often, you can add it to your phone's Home Screen from the browser's share menu and it opens like an app.
No. Tondavo has no accounts, sign-up or login. If you buy Pro, you unlock it by entering the email address you paid with, and that is the only time Tondavo sees an email address.
Any phone, tablet or computer with a speaker, a microphone and a current browser: iPhone, iPad, Android, Windows, Mac, Linux and Chromebook. Tondavo uses standard browser features (Web Audio, microphone access, WebAssembly and Web Crypto) that current Chrome, Edge, Safari and Firefox all support.
The sending device needs a working speaker. The receiving device needs a working microphone and permission to use it.
No. Tondavo doesn't need both devices on the same Wi-Fi network. Each device connects to the relay over its own connection, so a phone on mobile data and a laptop on office Wi-Fi work together. That is the main difference from AirDrop, LocalSend and Snapdrop, which need both devices on the same network. Both devices do need internet access for files. More: sending files between different networks.
Yes, for files and for messages longer than 120 characters: Tondavo needs an internet connection of any kind on both devices, because the encrypted file goes through the relay.
No, for short messages of up to 120 characters. Once chirpfile.com has loaded, a short message travels only as sound, with no network involved.
The devices need to be in the same room. In Silent mode, keep them within about 1 meter (3 feet). In Audible mode, a few meters usually works, depending on the speaker, the microphone and the noise in the room. Closer is always more reliable, and nothing works through walls.
No. Tondavo only works between devices in the same room, because the file's ID and key travel as sound from one device's speaker to the other's microphone. It's built for nearby devices on different networks, such as a phone on mobile data and a laptop on office Wi-Fi. To send a file to someone in another place, use a cloud storage link or a file-transfer service.
A chirp for a file or long message plays for about one to three seconds, because it carries only a short ID and the key. A short message is sent as sound in full, so one near the 120-character limit takes several seconds.
Silent, Audible and Dual are Tondavo's three ways of playing the chirp. Tap the speaker icon at the top of the app, next to the Pro button, to switch.
The frequency ranges come from the ggwave protocols Tondavo uses. The receiving device listens for all three modes at the same time, so only the sender chooses.
Start with Silent mode, the default. If the other device hasn't received it after two tries, switch to Audible. In a loud space, such as a café or an open office, use Audible or Dual from the start.
The receiving device needs chirpfile.com open with the microphone on: tap Tap to Listen, allow the microphone, and keep the page on screen. The page shows "Listening to room" while it can receive. Text appears in the thread as it arrives. Files appear as a card with a download button.
Yes for short messages: every device in earshot with Tondavo open decodes them.
Files go to one device by default, because a file is deleted from the relay after its first download. Persistent Mode, a Pro feature, keeps the file available for 15 minutes so every device in the room can download it.
Yes. For a few seconds after you send, Tondavo shows a replay button on the message. Replay plays the same chirp again without re-uploading anything. After that window, send the message or file again.
Yes. You can paste an image or a copied file into Tondavo on the sending device, and it is sent like a dropped file.
No. Tondavo doesn't keep a history of what you send or receive. The conversation lives only in the open browser tab and disappears when you close or reload it. Files you downloaded stay wherever your browser saved them.
Partly. Tondavo can send short messages of up to 120 characters with no connection once the page has loaded, but files and longer messages need an internet connection on both devices.
Yes. Tondavo is free for text of any length and for files up to 15 MB, with no account. Pro, at $0.99 for 24 hours or $4.99 a month, raises the file limit to 1 GB and adds batch sending and Persistent Mode.
No, Tondavo isn't open source. The code that matters for your privacy is visible and unminified, though: open the page source or the browser's developer tools and you can read exactly what runs, including the audit script that checks every outgoing request for the key. The sound encoding uses ggwave, which is open source under the MIT license.
Tondavo is safe against anyone who is not in the room, for files and for messages over 120 characters. They are encrypted in your browser with AES-128-GCM before upload, the relay stores only the encrypted copy, and the key travels only as sound. A hacked server, a snooped network or a forwarded link gets nobody the contents. There is no account to break into and nothing to install.
It does not protect against:
The full threat model is on the security page, and the zero-knowledge file transfer guide compares it with other designs.
No. Tondavo does not encrypt messages of 120 characters or less: they are played as sound exactly as typed. No server ever sees them, but anyone within earshot running a data-over-sound decoder could read them, since the encoding library is open source.
Don't put a secret in a short message. Save it in a text file and send the file instead, because files are always encrypted. Treat a short message like something said aloud in the room: quiet, but not secret.
No. Tondavo can't read your files, because it never has the key. The relay holds an encrypted copy it cannot open, and deletes it after the first download or after 15 minutes.
For a file or long message, Tondavo's relay sees:
It never sees the key, and it never sees short messages at all. Logging and retention details are in the privacy policy.
Tondavo holds encrypted copies in Cloudflare R2 storage. Each one is deleted the moment it is downloaded. If nobody downloads it, it can no longer be downloaded after 15 minutes, and a cleanup job physically deletes expired copies every 15 minutes. There are no backups and no archive.
Someone else can download your file only if they have both the file ID and the key, and both exist only in the chirp. The ID is random and can't be guessed.
Someone in the room who records the chirp could get both. Because the relay deletes a file on first download, whoever fetches it first wins, and the other device gets "not found". If your receiver ever says a file is gone when nobody else should have it, assume someone else took it.
A recording of a file's chirp is useful only for a short window: until the first download, or 15 minutes at most. After that there is nothing left to fetch.
A recording of a short message's chirp contains the message itself and can be decoded at any time. That is why short messages should never carry real secrets.
Tondavo uses AES-128-GCM through the browser's built-in Web Crypto API. Every transfer gets a new random 128-bit key. GCM also detects tampering, so a modified file fails to decrypt instead of opening corrupted.
We use a 128-bit key rather than 256 because the key has to fit in a chirp, and a shorter chirp decodes more reliably. Guessing a 128-bit key by brute force is not practical with any known computing technology. The encryption does not protect against a compromised device or a recorded chirp, though.
No. Tondavo doesn't record audio. The microphone input is decoded in the browser as it arrives and then discarded. Nothing is recorded, stored or uploaded. You can confirm it in your browser's developer tools: no audio ever leaves the device.
Tondavo needs the microphone on the receiving device to hear the key. It asks on the sending device too, so that either device can receive, but sending works without it.
No. Tondavo uses no analytics, advertising or tracking scripts, and no cookies. The only thing it stores in your browser is the Pro token, if you activate Pro, kept in local storage so you don't have to activate again.
One caveat: the app page loads the Inter font from Google Fonts, so Google receives a font request that includes your IP address. Checked 25 September 2026. See the privacy policy.
Tondavo's web server keeps standard request logs: IP address, the page requested, browser user agent, referring page, host name and response time. They sit in our hosting provider's rolling log buffer. When you activate Pro, a masked form of your email (like an***@example.com) is logged. See the privacy policy.
Yes, you can check it yourself. The chirpfile.com homepage runs an open audit script that scans every outgoing request for the active key and raises an alarm if it ever appears. You can also watch the Network tab in your browser's developer tools during a transfer: the upload contains only encrypted bytes, and the key appears nowhere.
Not from people in the room, if the password is 120 characters or less: Tondavo sends short messages as unencrypted sound, so anyone nearby with a decoder could pick it up. That is fine for giving a guest your Wi-Fi password, which they are about to have anyway. For anything sensitive, put it in a text file and send the file, which is encrypted, or use your password manager's sharing feature.
If the upload fails, Tondavo shows an error on the sender and plays no chirp. Send it again. If the receiver hears the chirp before the upload has finished, it keeps checking for about 20 seconds before giving up.
If a Tondavo transfer doesn't arrive, check these in order:
Silent mode fails on some devices because their speakers, microphones or audio processing cut off frequencies above about 15 kHz, which is where Silent mode lives. Laptops and older phones are the usual cases. Switch to Audible mode; it uses a band every speaker and microphone can handle.
Not well: Bluetooth headphones and speakers usually break Tondavo transfers. When sending, the chirp plays into your headphones, so the other device never hears it. When receiving, a Bluetooth headset's microphone records at too low a quality to carry the tones, especially in Silent mode. Disconnect Bluetooth audio on both devices before a transfer.
Tondavo stops listening because browsers cut off the microphone for pages that aren't on screen, and Tondavo pauses on purpose when you leave. It starts listening again when you return. Keep the receiving page in front during a transfer.
Look for the site settings icon next to the address bar, open it, and set Microphone to Allow. Then reload the page.
If the browser itself has no microphone access, fix that in the device's privacy settings first.
"Not found" means the file was already downloaded, by another device or an earlier attempt, or the upload never finished. "Expired" means more than 15 minutes passed. In both cases, send it again.
Set the sending device to at least half volume, and louder in Silent mode, which loses more energy to the room than Audible. A chirp played at low volume simply isn't heard, and nothing warns you.
Yes, Tondavo usually works in noisy places if you use Audible or Dual mode and hold the devices closer together. Loud music and crowd noise in the same frequency range can still drown out the chirp.
If chirpfile.com is blocked, try chirpfile.up.railway.app, the same site on a different domain. Some company web filters wrongly classify chirpfile.com as cloud storage, and they usually classify the other domain differently. If your employer blocks file-transfer sites on purpose, follow their policy.
Tondavo uploads are almost always limited by your connection's upload speed. Hotel, conference and mobile connections often upload far slower than they download. Encryption itself adds a few milliseconds. Files over 95 MB are split into parts that upload in parallel.
Yes, Tondavo works in Safari and other iPhone browsers. Keep the screen on and the page in front while receiving, since iOS stops the microphone for background pages. Received files are saved through the browser's download, usually to Files › Downloads.
Russian, Chinese and emoji characters take up more room in the chirp than English letters. A short message near the 120-character limit in a non-Latin script can be too big to decode. Send a shorter message, or make it longer than 120 characters so it goes through the relay as an encrypted upload instead.
Tondavo sends files up to 15 MB free, and up to 1 GB with Pro. Long text messages have no practical limit.
As of September 2026, Tondavo Pro costs $0.99 for a day pass, which lasts 24 hours from purchase, or $4.99 a month. Payment is handled by Stripe.
Tondavo Pro includes:
No. Only the sending device needs Pro; any device can receive any file for free.
To activate Tondavo Pro, pay through the Pro link in the app, then enter the same email address in the Pro panel. Tondavo checks with Stripe and unlocks Pro in that browser. Activate it on each browser you send from.
Cancel Tondavo Pro from the "Manage billing" link in the Pro panel. It opens Stripe's billing portal, where you can cancel. The day pass doesn't renew, so there's nothing to cancel.
Yes, with Pro: Tondavo packs several files into a single zip and sends them together. On the free tier, send them one at a time, or zip them yourself first.
Not directly: Tondavo sends files, not folders. Zip the folder and send the zip, or with Pro select all the files inside it.
Persistent Mode is a Tondavo Pro feature. Normally a file is deleted after its first download. With Persistent Mode on, it stays available for 15 minutes, so every device in the room can download it from one chirp. Useful in meetings and classrooms.
Tondavo keeps a file available until its first download, or for 15 minutes, whichever comes first. With Persistent Mode, it stays for the full 15 minutes.
No. Tondavo has no daily or monthly limit on the number of transfers, on either tier.
For a phone-to-PC transfer, use a USB cable if you have one: it's often the fastest option and needs no internet. Without a cable:
Without a USB cable, use AirDrop between Apple devices, Quick Share between Android and Windows (or between supported Android phones and Apple devices), LocalSend when both are on the same Wi-Fi, or Tondavo when they're on different networks or you can't install anything. Cloud storage (iCloud, Google Drive, OneDrive) and emailing the file to yourself also work.
Phones can transfer files without Wi-Fi over their own direct radio link:
Yes, files can be transferred without internet using a USB cable, AirDrop, Quick Share, Bluetooth, or LocalSend over a phone hotspot. Tondavo needs internet for files, though it can send short text of up to 120 characters with no connection once the page has loaded.
To transfer files between two computers without the internet, use a USB drive or an external disk, an Ethernet cable between them, or a shared local network (Windows file sharing, AirDrop between Macs, or LocalSend). Tethering both to one phone's hotspot creates a local network if there is none. Tondavo isn't the right tool here: its files travel over the internet.
To transfer files between devices on different networks, use something that goes through the internet: cloud storage, email, a file-transfer link, or Tondavo, which needs no account and sends the key by sound. Local tools like AirDrop, LocalSend and Snapdrop find each other on the local network, so they can't see a device on another network. The cross-network guide explains why.
Yes. AirDrop, Quick Share and LocalSend send directly from one device to the other, and browser tools like Snapdrop and PairDrop connect browsers directly with WebRTC. All of them need the devices on the same network or within radio range.
Tondavo is not direct: the file goes through the relay, encrypted. That is exactly what lets it work across networks.
To send a large file to a device in the same room, use LocalSend if both are on the same network: it's fast and has no size limit. A USB cable or drive works anywhere. Tondavo Pro handles files up to 1 GB, but the speed is limited by your upload connection.
Rarely. Bluetooth file transfer is slow, needs pairing, and iPhones don't support sending general files over Bluetooth at all. Quick Share and AirDrop use Bluetooth only to find the other device, then switch to much faster Wi-Fi radio.
To move photos from an iPhone to a Windows PC:
If the Android phone supports Quick Share's AirDrop compatibility, use AirDrop from the iPhone: set Quick Share on the Android phone to receive from everyone, then pick it in the iPhone's AirDrop list. Otherwise, without installing anything, open chirpfile.com in a browser on both phones, tap Tap to Listen on the Android phone, and send the file from the iPhone. Both phones need an internet connection, and free files go up to 15 MB. LocalSend also works if both phones are on the same Wi-Fi and you can install it.
For a one-off transfer, open chirpfile.com in a browser on both devices, tap Tap to Listen on the iPhone, and send the files or photos from the PC. The devices can be on different networks, but both need internet, and free files go up to 15 MB each. For regular syncing, Apple's iCloud for Windows keeps files and photos in step through iCloud Drive and iCloud Photos. LocalSend works if both are on the same Wi-Fi and you can install it.
Use a USB cable, Quick Share for Windows, or Microsoft's Phone Link, which shows your phone's recent photos on the PC. LocalSend works if both are on the same Wi-Fi. For a few photos without installing anything, or across different networks, open chirpfile.com on both and send them, up to 15 MB each for free.
Quick Share for Windows is the simplest option when the phone is nearby. LocalSend works when both share a network, and a USB cable works anywhere. Without installing anything, or across different networks, open chirpfile.com on both, tap Tap to Listen on the phone, and send from the PC. Both need internet, and free files go up to 15 MB.
Phone videos are usually bigger than they look: an iPhone records about 170 MB per minute of 4K video at 30 fps. So for most videos use a USB cable, AirDrop (iPhone to Mac), Quick Share (Android to Windows), or LocalSend on the same Wi-Fi, none of which has a practical size limit. Tondavo handles videos up to 15 MB free, which fits only short clips, and up to 1 GB with Pro, at your upload speed.
Supported Android phones can now send files to a Mac through Quick Share's AirDrop compatibility. Otherwise, LocalSend on the same Wi-Fi, cloud storage, or Tondavo in the browser all work. A USB cable needs extra software on the Mac.
No. Apple doesn't make AirDrop for Windows. The usual substitutes are iCloud for Windows, LocalSend on both devices, or a browser tool. On the same Wi-Fi that means Snapdrop or PairDrop; across networks, Tondavo. See AirDrop alternatives.
Android's equivalent of AirDrop is Quick Share. Since November 2025, Quick Share can also send files to and receive them from AirDrop on supported Android phones: see which phones work with AirDrop.
An iPhone can AirDrop to an Android phone only if the Android phone supports Quick Share's AirDrop compatibility and is set to receive. With other Android phones, use LocalSend on shared Wi-Fi, or Tondavo in the browser.
There is no built-in way to AirDrop from an iPhone to Windows. Install LocalSend on both if you do it often on the same Wi-Fi. Use Tondavo in the browser for an occasional transfer, a work PC you can't install on, or devices on different networks. Full comparison: AirDrop alternatives.
AirDrop is Apple-only. It sends directly between devices, is fast, has no size limit, and needs no internet. Tondavo works between any devices with a browser and across different networks, but files go through an encrypted relay, need internet, and are limited to 15 MB free or 1 GB with Pro. Between two Apple devices, AirDrop is the better choice.
AirDrop usually can't find a device because of one of these settings. Check that:
Switching the receiver to Everyone for 10 Minutes fixes most cases.
LocalSend fails to find a device when the two can't see each other on the local network. That happens when:
Fixes: put both on the same network, set the network to Private on Windows, turn off the VPN, or connect both to one phone's hotspot. If none of that is possible, Tondavo works across networks.
LocalSend doesn't need the internet, but it does need a shared local network. Turning on one phone's hotspot and connecting the other device to it is enough. With no shared network at all, it can't work.
No. LocalSend only works when both devices are on the same local network, because it finds them by broadcasting on that network. For fixes and alternatives, see LocalSend on different Wi-Fi.
LocalSend on iPhone usually fails because of iOS's Local Network permission. Go to Settings › Privacy & Security › Local Network and turn LocalSend on. Keep the app open in the foreground while receiving, and make sure both devices are on the same network.
PairDrop shows other devices automatically only when both are on the same network. For devices on different networks, pair them with a code or join a public room. Some networks also block the direct browser connection PairDrop relies on. Step-by-step fixes: PairDrop not seeing devices.
PairDrop is a fork of Snapdrop. Both send files between browsers on the same network. PairDrop adds pairing and rooms for connecting devices on different networks.
LocalSend is a free, open-source app. It sends files directly on the local network, fast and with no size limit, but both devices need the app and the same network. Tondavo needs no install and works across networks, but files go through an encrypted relay with size limits. If both devices share Wi-Fi and you can install apps, LocalSend is the better tool.
Hotel and other public networks turn on client isolation: every device can reach the internet but not other devices on the same network. It protects guests from each other, and it also stops AirPlay, Chromecast, LocalSend and other local sharing. More in hotel Wi-Fi file transfer.
AP isolation, also called client isolation, is a router setting that blocks devices on the same Wi-Fi from talking to each other directly. Each device can still reach the internet. Public and guest networks use it so strangers can't reach your laptop. On your own router you can usually turn it off; on a hotel's, you can't.
Hotel Wi-Fi usually blocks your devices from reaching each other, so use a USB cable, your phone's hotspot with LocalSend, cloud storage, or Tondavo, which works because each device reaches the internet on its own and the key goes by sound. Details: hotel Wi-Fi file transfer.
Hotel Wi-Fi operators can see which sites you connect to and how much data you move, but not the content of HTTPS pages, which is nearly all of them. A VPN hides even the site names from the hotel. With Tondavo, they could see that you connected to chirpfile.com, but the file itself is encrypted twice: once by Tondavo and again by HTTPS.
Usually: guest networks block file sharing between devices. They typically isolate devices from each other and sit on a separate network from the main one, so local sharing tools can't cross. Tools that go through the internet, like cloud storage or Tondavo, still work.
A VPN breaks local file sharing because it routes traffic through a different network, so tools that look for devices on the local network often can't find them. Tondavo works with a VPN on either or both devices, because each device only needs to reach the relay.
Check your company's policy first: many companies forbid moving work data to personal devices, and their security software often logs USB use, uploads and the websites you visit. If it's allowed, use a company-approved tool like OneDrive, Teams or work email. Tondavo works on locked-down laptops because it needs only a browser, but it is visible to IT and is not a way around company rules. More: transferring from a corporate laptop.
Often, yes: employers can usually see file transfers from a work laptop. Company laptops commonly run monitoring and data-loss-prevention software that can log files copied to USB drives, uploads to websites and the sites you visit. Using Tondavo doesn't hide that activity. The file's contents are encrypted, but the fact that you used the site is visible.
To copy text from an iPhone to a Windows PC, open chirpfile.com on both, paste the text on the iPhone and send. Up to 120 characters travels as sound alone, with no network, and appears on the PC with a copy button, but short messages are not encrypted. Longer text goes through the encrypted relay. It works the same from PC to iPhone.
Other options: email or message the text to yourself, use iCloud Notes at icloud.com, or use Snapdrop or PairDrop if both devices are on the same Wi-Fi.
To copy and paste between Android and Windows, use Microsoft's SwiftKey keyboard on Android, which can sync your clipboard with Windows clipboard history once you sign in to the same Microsoft account on both. For a one-off without setup, Tondavo works in both browsers.
To send a link from your phone to your computer, paste it into Tondavo on the phone and send. A link under 120 characters goes as sound and arrives as a clickable link. If you use Chrome signed in on both devices, its "Send to your devices" feature also works.
Yes: Tondavo can send up to 120 characters of text between devices with no internet, once chirpfile.com has loaded on both. The text travels only as sound. Short messages are not encrypted, so anyone nearby with a decoder could read them.
A Tondavo text message has no practical length limit. Up to 120 characters goes as sound alone. Anything longer is encrypted and sent through the relay, with only the key going as sound.
On iOS 18 or later, share a Wi-Fi password from iPhone to Android with a QR code: open the Passwords app, tap Wi-Fi, choose the network and tap Show Network QR Code. The Android phone scans it with its camera and joins. Or copy the password from the same screen and send it with Tondavo. More: sharing a Wi-Fi password.
Only between Apple devices, and you rarely need to: when a contact's iPhone tries to join your network, your unlocked iPhone offers a Share Password button. You can also AirDrop a saved password from the Passwords app. Neither works with Android; use the network's QR code instead.
Use a shared vault in a password or secrets manager, so the secret never sits in a chat. One-time secret links are the next best option, though the link itself still travels over chat or email. If you're in the same room, Tondavo keeps the secret out of every chat log: send it as a text file or as a message longer than 120 characters, so it is encrypted (short messages are not). Rotate the key if you think it was exposed. More: sending an API key securely.
Avoid sending passwords over Slack or email when you can. The message stays in history, gets indexed for search, lands in backups, and is exposed if either account is compromised. Use a password manager's sharing feature or a one-time secret link instead. If you must use chat, delete the message afterwards and rotate the password later.
Yes. Tondavo can send a one-time code as sound, with no network. The code is not encrypted, so only do it in a room you trust.
Data is sent through sound the way an old modem does it. Each piece of data is turned into a combination of tones at specific frequencies, played through a speaker. The receiving microphone listens for those frequencies and turns them back into data. Error-correcting codes let the receiver fix bits lost to noise. The acoustic data transmission guide goes deeper.
ggwave is an open-source data-over-sound library by Georgi Gerganov, released under the MIT license. Tondavo uses it to encode and decode chirps. Its author also makes Waver, a demo app for sending messages by sound.
Data over sound is very slow: tens of bytes per second with ggwave's protocols. That's why Tondavo sends only a short ID and key by sound, and moves the file itself over the internet.
Sending a whole file over sound would take far too long. At tens of bytes per second, a 1 MB photo would take hours of continuous chirping in a silent room. Sending only the key keeps the chirp to a second or two while the file moves at internet speed.
Yes in Audible mode, where the chirp sounds like a quick burst of beeps. In Silent mode most adults hear nothing, but children and some young adults can hear a faint high-pitched sound, since it sits between 15 and 19.5 kHz.
Tondavo's chirp is ordinary sound from your device's speaker, at the volume you set, for a second or two. Dogs and cats hear the Silent-mode range easily, though. If a pet reacts to it, use Audible mode.
No. Tondavo doesn't work through walls: the devices need to be in the same room. It doesn't work reliably over a phone or video call either. Calls compress audio and cut off high frequencies, so Silent mode can't pass at all. And sending the key over a call would put it on a network, which defeats the point.
Other apps that send data over sound include Waver, built on ggwave, which sends messages between phones and computers. LISNR sells data-over-sound for payments and ticketing. Chirp, a data-over-sound company, was bought by Sonos in 2020. Google's Nearby used near-ultrasonic tokens to detect nearby devices.