PairDrop uses WebRTC peer-to-peer. When NAT, firewalls, AP isolation, or different networks block the handshake, the two devices can show online but never actually connect. Here's the diagnostic path and the workaround.
Quick fixes to try first
Refresh both browser tabs. PairDrop's signaling can hang. A clean reload often re-establishes the WebSocket.
Disable VPN on both devices. VPN endpoints often break WebRTC's NAT traversal. Many WebRTC failures are pure VPN problems.
Try a different browser. Safari's WebRTC implementation is more restrictive than Chrome/Firefox. If one browser fails, the other sometimes works.
Same WiFi check. Confirm both devices are on the same SSID and the same subnet. Guest networks and 5GHz/2.4GHz split networks can look identical but route differently.
Disable AP isolation if you control the router. Some consumer routers enable this by default. The setting is usually under wireless security.
What's actually happening
1. PairDrop uses WebRTC for transfer
The PairDrop website is a signaling server. It tells both devices about each other. The actual file transfer happens over a direct WebRTC connection between the two devices. No server-side relay carries the bytes.
2. WebRTC requires NAT traversal
To open a peer-to-peer connection across the internet, WebRTC uses ICE (RFC 8445) plus STUN servers to discover external IP/port mappings, and TURN servers as a fallback relay. If STUN can't determine reachable addresses or TURN is blocked, the connection fails silently.
3. Many networks block this
Corporate firewalls often block STUN/TURN ports. Hotel and guest WiFi blocks UDP ranges. Symmetric NATs (common on mobile carriers) defeat STUN entirely. AP isolation prevents same-network peer connection. VPN endpoints break the connection mid-handshake.
4. So you see both devices, but the transfer doesn't happen
The signaling layer works (both devices appear in PairDrop's UI). The transfer layer doesn't (the actual WebRTC channel never opens). This is the most common "PairDrop not seeing device" symptom.
When PairDrop is structurally going to fail
Some scenarios just don't work with peer-to-peer architecture, no matter what you try:
Phone on cellular, laptop on WiFi. Two different NATs. Mobile carrier NAT is usually symmetric, which defeats STUN.
Hotel or corporate WiFi. AP isolation blocks peer connection. UDP ports often blocked by enterprise firewall.
VPN active on either device. WebRTC NAT traversal fails through most VPN endpoints.
Large files (>200 MB) on mobile. WebRTC's congestion control plus mobile network jitter causes frequent mid-transfer failures.
The workaround: don't use peer-to-peer
The structural issue is that PairDrop's transfer requires a direct connection between two devices that may not be reachable to each other. If you take peer-to-peer off the table entirely, the network constraints vanish.
chirpfile uses a regular HTTPS upload to a relay - same path as any web request. The decryption key travels between the two devices as sound (1-2 seconds of audio). No WebRTC, no STUN/TURN, no peer handshake. If the device can load a webpage, it can send and receive.
An honest comparison. PairDrop is free and faster than chirpfile for same-network transfers - use it when WebRTC works. chirpfile is for the situations where WebRTC structurally won't: NAT issues, AP isolation, VPN active, mobile carriers, large files on mobile, hotel/corporate WiFi.
Try it now
Open chirpfile.com on both devices. Drop a file. Listen for the chirp.
What's the difference between Snapdrop and PairDrop?
PairDrop is the community fork of Snapdrop (Snapdrop.net was acquired by LimeWire). Same WebRTC architecture, same network limitations. If PairDrop fails on your network, Snapdrop will fail the same way.
Why doesn't PairDrop just use a server relay when peer-to-peer fails?
It does have TURN servers as fallback, but TURN is bandwidth-expensive and often blocked by the same firewalls that block STUN. PairDrop's primary value proposition is peer-to-peer privacy; falling back to a server defeats it.
Does chirpfile see my file like a TURN relay would?
No. The file is encrypted in your browser before upload. The relay holds ciphertext it cannot read. The decryption key never touches the network - it travels as sound. There's an audit panel at the bottom of every chirpfile page that lets you verify this in real time.
Does chirpfile work on hotel WiFi where PairDrop fails?
Yes. chirpfile only needs each device to reach a regular website over HTTPS. Hotel WiFi blocks UDP and peer-to-peer, but it almost never blocks HTTPS. The acoustic key transfer happens between the two devices directly, no network needed for that step.
What's the file size limit?
Free tier is 15 MB. Pro tier is 1 GB. Text under 120 characters (passwords, URLs, codes) bypasses the relay entirely - pure sound, no upload.