I managed to install watchOS 2 without having registered my Watch's UDID, but as it's part of the instructions for installing watchOS betas I thought I'd better do it now in case beta 2 bricks my Watch or something.
However, the Watch isn't appearing in Xcode. I've tried both the latest public release and Xcode 7 beta, but there's "no paired devices" section under my iPhone when I connect it to Xcode and look in the Devices window.
Try unplugging your phone from the USB, and then reconnecting it.
Does iTunes see it? If you run System Profiler, does it show up there in the USB group?
If you're connecting via a USB hub or external HD, try connecting it direct to your computer, instead. As well, you may need to restart your computer so the USB chain can take a fresh look at connected devices.
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Did you ever get the 'trust this computer' dialog on the watch? If not you'll need to un-pair and then re-pair the Watch with your iPhone. Then re-start Xcode and it can take about a minute or longer for the watch to showup the first time.
With Watch OS 10.1 and Xcode 15.0.1 I was facing the same issue. After spending the whole night the issue was my Mac's Bluetooth, it was turned off and I spent all night finding the fix. Turning Bluetooth on solved the problem. Developer Mode showes up in Privacy & Security and everything worked fine.
I have literally done everything on the list of comments and also reset my watch. Still no developer mode showing on my watch, I have the Ultra 1, it makes it incredibly hard to test my app without having a physical device, I need to test the vibrations too. Beyond frustrating, unsure why Developer mode needs to be hidden away in the first place as it's clear enough from all the pop ups etc. any person who doesn't need it isn't going to accidentally activate it.
I read this advice somewhere else but it worked for me: unpair your phone from Xcode, and reconnect via cable on a different USB slot, it will ask again whether you trust the devices. Than developer mode appeared on the wacth and could select the device on Xcode. I had transfer issue and, that was solved by reconnecting to wifi and bluetooth, both on the laptop and watch.
I am so angry that I still can't connect the watch. I have tried all methods