The Baby Doppler
I have a OB nurse friend who had one for her pregnancies, in addition to being a nurse she's pretty crunchy and alt-health minded and didn't seem hesitant about it at all. She'd check on her son a couple of times a day.
That said it is considered medical equipment (I think you still need a script/permission from your doctor to get one in the first place, unless you're getting it second hand I guess) so if you're nervous I'd talk to the Doc/Midwife first. In general I think similar to an ultrasound it's a good idea to limit the length of use to somewhere around <20 minutes and not going too overboard with it.
Last time around I asked my SIL midwife about getting approved for one and she advised that as an "amateur" listener I was more likely to get myself worked up over not finding it, than I was to comfort myself or enjoy it.
This is the kind that she gave us- http://www.fairhavenhealth.com/fetal-doppler.html it's called an AngelSounds Fetal Doppler but we live in Canada so she probably paid more than $30 for it. It was super easy for my husband and I to find the baby's heartbeat. And honestly I don't think I would really freak out if I couldn't find it because I just heard it at the doctor's office the other day.
I got a doppler 10 years ago with my first and used it almost every day (after I found the HB myself at 9 weeks) until I felt movement regularly. I used it with my second less frequently, like a few times a week and with this one maybe once a week. My first two were born with no ill effects. I have had two losses (never heard the hb with the doppler with those), so I just use the doppler to reassure me when I convince myself that something is wrong.
On the other hand you google "doppler" use you will probably find some information saying it can possibly cause harm.Read all the information (keeping in mind that not everything you read on the internet is accurate) and decide what is best for you. I think moderation is key.
If you do use it, a few words of advice- depending on how far along you are and the position of the baby and your placenta, you may not find it. Even my midwife had trouble finding the HB last time- he was just hiding and she kept picking up my placenta. So unless you are having signs of a miscarriage, don't freak out!
Also often you will hear your own pulse- check your pulse while listening to the heartbeat- if it is the same, it is yours. Baby's heartbeat sounds more like galloping horses. Many a mom has been freaked out thinking something's wrong because the heartbeat was low, only to find she was picking up her own pulse in a blood vessel.
AFM I'm looking forward to when I feel movement regularly- then I know baby's doing ok in there.
I have seen doctors cautioning also because the mom thinks everything is fine when it might not be. I am not sure that is a good enough reason not to use them but listen to your body, continue doing kick counts (when we get that far), etc... don't rely solely on what you hear.
you don't need a script to get one ..you can one off ebay. but you need a good one..the one from Babies r us does not work. IF you decide to use it..I would just use it once a day for less than a minute .. that should not hurt your baby. when you feel movement, then stop. or even once every few days shouldn't hurt.. but with anything, I would use caution, and only when you think you too :)