I missed your OP, darcy, sorry about that, but if you were referring to fetal dopplers? I own one, too. I bought it around 14 wks. or so, from eBay, b/c my anxiety level being pg for the first time after a m/c was really high and I needed to calm down!
I only listen once a week, usually, and now that the baby is starting to move more regularly, I'll probably cut back even more until 3rd tri, when I'll get paranoid again, no doubt
(my 5th child was born via emergency c/s at 35w b/c she went into fetal distress in utero and stopped moving.)
For me, though, it's been a godsend. I don't listen long, just long enough to make sure it's the bean I'm hearing and not me, but I sleep better at night and my BP is much better overall after I've heard that precious whoosh-whooshing. I feel a bit guilty b/c my baby clearly does not enjoy the doppler -- he/she swims away from it all the time and often kicks me as if to say, "Hey, Mom, cut that out!"
: However, I have accepted that one of the things about my journey in pg after loss is my significantly increased need for reassurance; hopefully, baby bean will forgive me for my deeply-seated need to keep closer tabs!