I have one for my bleeding disorder and bronchiectasis. When I had a massive hemoptysis, there was a lot of initial talk about whether it was blood from my stomach. I knew it wasn't and was able to speak, but I don't want them wasting time if I am ever unable to speak.
I recommend getting one that is good quality and that you won't wnat to take off here and there. At first, I got a cheaper one and it broke because it couldn't stand the wear and tear of constant use. Now I have a sterling silver link one that looks pretty, cost about $70, and is totally waterproof.
I wish I could remember where I got it from...wait, email archives here I come:
www.creativemedicalid.com
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Melissa, 34, bronchiectasis (no CF)