Assuming you're in the US, my gut answer would be no. This is from 10 years of tax preparer experience.
There are a few reasons that I would say no. First there are cheaper devices that do the same thing. Also I'm not too sure if this would be a medical device that is FDA approved.
Then again, I could see a way to make an argument that the watch would be deductible/reimbursable for you.
Best ways to get something to count is to have your doctor prescribe it as part of a treatment regimen.
An extreme example of a deductible expense would be a hot tub. For people with extreme eczema, or other dermatology issue that can be treated with hot water, they can actually deduct the hot tub so long as their doctor prescribes it.
Again, I would say no, it doesn't really pass the sniff test; but worse case is you can't get the reimbursement through your fsa. If you have a heart/weight/etc issue, you could at least go for it.