Fetal doppler question

I just got my fetal doppler in (a sonoline B) and was wondering if anyone had ever heard that they were harmful to use? OR if anyone has used one throughout their pregnancy and had a healthy, happy baby! I ordered the doppler because I am almost 12 weeks preggo, and also a worrier, so it makes me feel better to hear the babies heart beat a couple times a week.  Although, just recently I have had people  ask "are you sure that it's safe for the baby?" And it's made me wonder... Any comments are greatly appreciated!