DD is 2 1/2 so it's been ages since I looked up this stuff.
If my mom hadn't flipped, I wouldn't have worried so much. DH and I are also heavy sleepers. DD also slept through the night starting at 3 weeks or so - so sometimes I would go in to see that she was ok. With all of these factors, I didn't want the extra worry.
You should be able to find them at almost any health / cloth diaper store. Even grown ups wear them to alleviate pain.
I've read that these necklaces were almost equivalent to taking Tylenol.