Offline file sharing from a screen to a camera

How air-gapped file sharing works

An air gap separates a device from network connections. A screen-to-camera transfer can carry content across that gap: the display shows the file or text as animated patterns, and the receiving camera reads those patterns. The transfer itself needs no Wi-Fi, mobile data, Bluetooth, cable, or connection to Held’s servers.

Held’s web setup requires each browser to load the tool online before offline use. It is not a ready-to-use solution for a device that must never connect to the internet. You are responsible for disconnecting the devices; Held does not establish or verify their isolation.

Prepare both browsers before disconnecting

Open Optical transfer at held.cat/qr on each device while connected. Wait until both show Available offline. Readiness applies to that browser on that device; another browser or cleared site data needs its own setup. The receiving browser must support camera access.

After preparation, reopen the same /qr address in the prepared browser while offline. No separate offline page or app installation is needed. Test the setup on your devices before relying on it.

Send a file or text offline

Each transfer holds one file or plain text up to 16 MiB. For text, this limit counts UTF-8 bytes. The mode is experimental; speed and successful reception depend on screen size, camera quality, focus, lighting, and keeping the pattern visible.

1. On the sending device, choose Send, then File or Text, and select a file or enter your text.
2. If you need encryption, enable Protect with a password before choosing Show transfer patterns.
3. On the receiving device, choose Receive and Start camera, then keep the full pattern in view until reception finishes.
4. Enter the password if one was set. Download the verified file, or copy the received text or save it as a .txt file.

Choose whether to encrypt the optical transfer

Password protection is optional and off by default. When enabled, it encrypts the content and file name in the sending browser. Use a strong password of at least 6 characters and share it separately. The receiver collects the transfer before entering the password to unlock it.

Without password protection, any camera that records enough of the patterns can recover the content. Encryption does not authenticate the sender’s identity, make an untrusted device safe, or erase saved copies. Recipients keep any files or text they save.

When to use optical or peer-to-peer file sharing

Use Optical transfer when a prepared device needs a small file or text handoff without a network connection. The receiving camera must be able to see the sending screen.

Use regular encrypted peer-to-peer file sharing for larger files between connected browsers. Messages, group chat, and nearby File transfer require network access. QR device pairing shares an invitation for one of those network transfers; Optical transfer carries the content itself.