I rented my monitor from StorkRadio and it's actually the same model my midwife uses. I am generally able to find the heartbeat pretty quickly, but I didn't start trying til about 14 weeks. And it's always waaay down low. Like an inch above the pubic bone. There were a few times I couldn't find it right away, and when I did, it was very faint. I think he was just rotated at some weird angle that day, so I couldn't get a clear sound. Like the others have said, it could also be the monitor itself not being sensitive enough.
Not only is it the monitor,it's the way the baby is lying and how good you are at finding the baby. I first found my babies HB at about 17 weeks. I still have a hard time locating it and I am 24 weeks. The Dr just feels my tummy and Voila 1st hit she finds it. Don't worry if it takes some time, soon enough you will become an expert or get to the point where you feel movement. Also if you have a tilted uterus or the placenta lies in front the HB becomes harder to find.
Which monitor is the best to get?
It's the quality of the monitor. I am almost 15 and all week have heard it...sometimes takes a little practice
An OB was able to find my babies at about 10 weeks. I have a really good quality doppler (I took it in to my Dr. to check out) and really didn't have much luck with it until about 14 weeks. Even then, it was hit and miss at best...some days I found it quite easily, other days it took awhile or not at all. I don't think I got really consistant with it until 16 weeks or so. Remember that not only are they tiny at this stage, they are moving around all over the place. It can be tough, and you are early still. Don't let it scare you...personally I would put it away until at least 14 weeks. Good luck.