Apple's connection article treats a missing sync as a disconnected watch. If a red iPhone icon shows on the watch, or you get no notifications, messages or calls, the watch and iPhone are not connected; when they reconnect the icon goes away. Bring them close together, then on the iPhone open Control Center and make sure Airplane Mode is off and Wi-Fi and Bluetooth are on; on the watch press the side button and make sure Airplane Mode is off.
Check after each step. If that fails, unpair the watch and pair it again, which restores from the backup the iPhone made. Activity, workouts and health data sync through the iPhone, so an unconnected watch keeps them and sends them later. Apple's cellular article adds that on GPS + Cellular models a watch away from the iPhone can use Wi-Fi or cellular, and that some apps do not update without the iPhone connection.
Differential
Likely causes of “Apple Watch will not sync activity or data”, and how to tell them apart
- 1
Airplane Mode is on, on either device
What separates it A red iPhone icon shows in Control Center because Airplane Mode is on, on either device
How to confirm Turn Airplane Mode off on both devices, and check the link
- 2
Bluetooth or Wi-Fi is off on the iPhone
What separates it Data will not move and notifications arrive on the phone only
How to confirm Turn both on in the iPhone's Control Center
- 3
The watch is out of range
What separates it The link drops when the phone is in another room
How to confirm Bring them close and wait for the ping
- 4
A stale link after an update
What separates it The connection fails after a watchOS or iOS update
How to confirm Restart both devices, then re check the link
- 5
A corrupted pairing
What separates it Nothing fixes the link because of a corrupted pairing between the devices
How to confirm Unpair and pair again, restoring from the backup
Before you touch a setting
Record this first — changing settings destroys the evidence
- The model number, watchOS version and iOS version
- Whether a red iPhone icon shows on the watch or in Control Center
- What data is missing: activity, workouts, notifications or health readings
- Whether the watch has cellular and reaches the internet on its own
Try in this order
0 of 7 completedBring the devices together
ReversibleBring the devices together, by keeping the watch and iPhone close and waiting a moment for the connection.
Check the iPhone
ReversibleOpen Control Center on the iPhone. Turn Airplane Mode off and Wi-Fi and Bluetooth on.
Check the watch
ReversibleCheck the watch, by pressing the side button and turning Airplane Mode off, and then test again to see whether it helped.
Look for the red icon
ReversibleThe red iPhone icon in Control Center means not connected. When it disappears the devices are connected.
Restart both
ReversibleRestart both, by restarting the iPhone and the watch, and re checking the link, and then test again to see whether it helped.
Ping the watch
ReversiblePing the watch, by using Ping Watch from the iPhone's Control Center to test the link.
Unpair and pair again
ReversibleIf it still fails, unpair from the Watch app and pair again, restoring from the backup.
Model-specific
What is true of this model and not of its siblings
- Wi-Fi by model
- Apple's specs list 802.11b/g/n on 2.4 GHz and 5 GHz for the Series 6, 7, 8 and Ultra and Wi-Fi 4 (802.11n) for the Series 10, Ultra 2 and SE 2; Apple's cellular article says the Series 5 and earlier and the first SE support 2.4 GHz only.
- Bluetooth by model
- Bluetooth 5.3 on the Series 8, 10, Ultra, Ultra 2 and SE 2, and Bluetooth 5.0 on the Series 6 and 7, per Apple's tech specs.
- Repair cost
- Reconnecting and re-pairing cost nothing. A watch that will not connect after a force restart, unpair and re-pair is a hardware fault, quoted by Apple after diagnosis; Apple's battery service is $99, per 9to5Mac, and launch-day repair fees ran from $199 for an SE 2 to $499 for an Ultra, per MacRumors.
- Other models this page answers
- These steps also fit the Apple Watch Ultra 2, Apple Watch Series 8, Apple Watch Series 7.
Stop boundary
When this stops being a self-service repair
- !If unpairing fails or the watch cannot reach the iPhone after a force restart, book Apple service
- !If the iPhone cannot see Bluetooth devices at all, troubleshoot the iPhone
- !If the backup fails during unpair, stop and contact Apple before erasing
Evidence ledger
Sources behind this answer
The red iPhone icon, range, Airplane Mode, Wi-Fi and Bluetooth checks and unpair and repair.
How the watch chooses Bluetooth, Wi-Fi or cellular.
What unpairing does and how the backup works.
The reset routes if unpairing stalls.
The Apple Watch line and its generations.
Exact questions
Common questions
What does the red iPhone icon mean?+
Apple says it appears in Control Center when the watch and iPhone are not connected. It goes away when they reconnect.
Does my activity data survive a disconnect?+
The watch keeps it and shares it when it reconnects. Do not unpair before it has synced.
Why do notifications go to the iPhone instead?+
Apple says when the watch and iPhone disconnect, notifications go to the iPhone.
Can the watch work away from the iPhone?+
Yes, on Wi-Fi, and on GPS + Cellular models over cellular, though some apps need the iPhone.
Will unpairing lose my data?+
Apple's process backs up the watch first and you can restore from that backup.
Does Wi-Fi 5 GHz matter?+
Apple lists 2.4 GHz and 5 GHz for the Series 6, 7, 8 and Ultra, and Wi-Fi 4 (802.11n) for the Series 10, Ultra 2 and SE 2.
Why does the connection drop when I leave my phone?+
The watch falls back to Wi-Fi or cellular. A watch without those cannot sync until it is back near the phone.
What about a second watch?+
One iPhone can pair with several watches, but one watch pairs with one iPhone.