We've known about the Apple Watch since September, and between its introduction and release numerous enterprising folks have announced all manner of accessories for the Watch. Until this past weekend, though, few (if any) of those inventors have had the opportunity to touch and use the Watch. I've been aware of many of these accessories, too, and as soon as I started using the Watch one thing became clear: any accessory that separates the watch from your wrist will likely not succeed.
Apple Watch uses its backside sensors to do all sorts of things, including monitoring your heart rate. They also monitor whether the Watch is on – and remains on – your wrist. This is handy for a few things, including the Watch's unlocking mechanism. After you've unlocked the Watch once while on your wrist, it remains unlocked until it senses that it has been removed from your wrist. That's smart thinking on Apple's part, especially considering Apple Pay requires you to have a passcode set. There's even a setting that allows your iPhone to unlock your Watch but this, too, is predicated upon it being – and staying – on your wrist.
What happens when you have an accessory that separates your Watch from your wrist? I've tested this by inserting a thin, opaque piece of cloth underneath my watch. With this in place the Watch does not remain unlocked and asks for my passcode every time I try to use it. I would assume the same would be true for battery/charging straps or "NATO" straps, too. (As an aside, with the cloth in place I measured my resting heartrate at 174 - not good!).
It's important to remember that Apple designed the Watch such that the screen is expected to be off more than 99% of the time. It regularly monitors your activity and heart rate even in this state, but the screen is only built to power up when you raise your Watch or otherwise attempt to interact with it. This means things like bicycle mounts that would theoretically allow your watch to be seen on your handlebars while riding aren't likely to work very well. With the screen off – and the watch perpetually falling back into unlock mode – this is not the user experience you're likely going to want.
Over time there will undoubtedly be some fantastic Apple Watch accessories, and I'm sure some of the pre-announced items will fall into that category, too. Just beware anyone or anything claiming to add functionality to the Apple Watch with some gadget that separates it from your wrist. It's probably not going to work well, if at all.