It uses a P2P connection if WebRTC is supported by the browser. WebRTC needs a Signaling Server, but it is only used to establish a connection and is not involved in the file transfer.
If your devices are paired and behind a NAT, the public TURN Server from [Open Relay](https://www.metered.ca/tools/openrelay/) is used to route your files and messages.
None of your files are ever sent to any server. Files are sent only between peers. PairDrop doesn't even use a database. If you are curious have a look [at the Server](https://github.com/schlagmichdoch/pairdrop/blob/master/index.js).
If your devices are paired and behind a NAT, the public TURN Server from [Open Relay](https://www.metered.ca/tools/openrelay/) is used to route your files and messages.
Yes. Your files are sent using WebRTC, which encrypts them on transit. To ensure the connection is secure and there is no MITM, compare the security number shown under the device name on both devices. The security number is different for every connection.
Naturally, if traffic needs to be routed through the turn server because your devices are behind different NATs, transfer speed decreases.
As the public TURN server used is not super fast, you can easily [specify to use your own TURN server](https://github.com/schlagmichdoch/PairDrop/blob/master/docs/host-your-own.md#specify-stunturn-servers) if you host your own instance.
Alternatively, you can open a hotspot on one of your devices to bridge the connection which makes transfers much faster as no TURN server is needed.
- [How to open a hotspot on Windows](https://support.microsoft.com/en-us/windows/use-your-windows-pc-as-a-mobile-hotspot-c89b0fad-72d5-41e8-f7ea-406ad9036b85#WindowsVersion=Windows_11)
- [How to open a hotspot on Mac](https://support.apple.com/guide/mac-help/share-internet-connection-mac-network-users-mchlp1540/mac)
- [Library to open a hotspot on Linux](https://github.com/lakinduakash/linux-wifi-hotspot)
You can also use mobile hotspots on phones to do that.
Then, all data should be sent directly between devices and your data plan should not be charged.
Snapdrop and PairDrop are a study in radical simplicity. The user interface is insanely simple. Features are chosen very carefully because complexity grows quadratically since every feature potentially interferes with each other feature. We focus very narrowly on a single use case: instant file transfer.
We are not trying to optimize for some edge-cases. We are optimizing the user flow of the average users. Don't be sad if we decline your feature request for the sake of simplicity.
If you want to learn more about simplicity you can read [Insanely Simple: The Obsession that Drives Apple's Success](https://www.amazon.com/Insanely-Simple-Ken-Segall-audiobook/dp/B007Z9686O) or [Thinking, Fast and Slow](https://www.amazon.com/Thinking-Fast-Slow-Daniel-Kahneman/dp/0374533555).
