For all the Pregnant Women or ones who have already had a Child

Do you believe in using Dopplers to hear your baby's heart beat? I was thinking of buying one but a nurse at the hospital I was in told me that they annoy the baby. She said they hear it much louder than we think and that is why when she does sonograms the baby moves about trying to swipe at the Doppler or get away from it. If anyone knows more on this subject please share....Thanks.