Technically if you live in the states you need a prescription to get one because other wise its illegal. Now with that said-there are a few places you can get one. They aren't illegal because they are dangerous its just a loop hole so that people can arrest midwives (not certified) if they want to

It rarely is enforced and a few places will give you one anyway. A few doctors don't want you to have them because they tend to cause more trips to the doctors/worry poor mom's when they can't find a heartbeat at times (and those babies do hide in there! LOL) so the idea is to prevent moms from having that happen. (but then I know people who would have gone to the doctor but their dopplers made them feel better so the didn't! goes both ways).