Recommendations for Doppler heartbeat monitor?

Ugh.

I had a trip to the hospital last night, because I though what turned out to be just gas was something much worse. My last pregnancy I did the same thing; went to the hospital because I had really bad gas pains and it turned out to be severe preeclampsia with a very sad ending.

I'm a little paranoid.

Everything checked out last night, but it didn't take long for the nagging worry to start again today. So short story aside, I've decided to buy a Doppler heartbeat monitor to help with some of the worry. Does any one have recommendations? I'm probably going to get it from Amazon (and even splurge on the shipping costs to get it shipped from the US to Canada because there is so much more variety).