No cloud, no account, no relay.

Finding each other

Your phone advertises itself on the local network over mDNS, and the Mac listens for it. Home and office networks break multicast in a dozen different ways, including client isolation, mesh gaps and segmented corporate Wi-Fi, so there are three fallbacks behind it: the last address that worked, a UDP broadcast probe, and finally typing the phone's address in by hand.

Discovery only finds a candidate; it never grants access. A device that hasn't been paired can only attempt a handshake.

Pairing

The first time two devices meet, they perform an ECDH key exchange and each derives the same short numeric code from the result. You compare that code on both screens and confirm. If someone were sitting between the two devices, the numbers would not match.

After you confirm, each device stores the other's public key (on the Mac, in the system Keychain). From then on they reconnect automatically. Synqed checks the stored public key, not the device name, so renaming a machine changes nothing and spoofing a name gets an attacker nowhere.

The connection itself

Everything after pairing rides a single encrypted TCP connection. Frames are encrypted with AES-256-GCM.

• Fresh keys every session.The session key is derived from both the long-term identity keys and a throwaway keypair generated for that one connection. Traffic captured today can't be decrypted by someone who steals a device key tomorrow.
• No silent downgrade. If a peer omits its ephemeral key, both sides refuse the connection instead of falling back to weaker keys, because that fallback is exactly what an attacker would try to force.
• Replay protection. Every frame carries a counter that is authenticated but never transmitted. A frame replayed from earlier in the conversation fails its authentication tag, and a tag failure tears the whole session down rather than resynchronising.

What leaves your network

Nothing. There is no Synqed account, no Synqed server, and no relay. Your messages, notifications, files and clipboard travel from one of your devices to the other and stop there.

The one place Synqed touches the internet is checking for updates and fetching this site's download. The daily notification digest is generated on your Mac by Apple's on-device models, and the notification text is not sent to Apple or to us.

If you turn on AI assistants, which is off until you do, an assistant on your Mac can read what Synqed syncs. What it reads goes to that assistant's model, the same as anything you paste into it. Synqed itself still sends nothing anywhere.

What Synqed deliberately doesn't do

These are real limits, not features on the way. We list them because overstating what a product does is worse than doing less.

• Call audio stays on your phone. You can answer, decline, mute and redial from the Mac, but the audio never comes to it. That would need a full VoIP bridge, which is out of scope.
• Contacts are read-only. They sync to the Mac so you can search and dial. Editing a contact on the Mac does not write back to the phone.
• It only works on the same network.There is no out-of-LAN mode, because there is no relay server. Your phone's hotspot counts, though: put your Mac on it and the two connect wherever you have mobile signal.
• Notification dismissal is one-way.Dismissing on the phone clears the Mac. macOS gives no signal when a banner is dismissed without being clicked, so the reverse isn't possible.

Permissions

Synqed asks for a lot on Android, because mirroring a phone means reading what the phone does. The privacy policylists every permission and exactly what it's for.