tenar- a doppler is a device where you can listen to bubs heartbeat and hear him or her moving around. You can use it after 12 weeks, or for me it was 13 weeks. Any earlier and you probably wont hear anything.
Just go to ebay and type in doppler, I have the angelsounds one. I think mine cost about $60, but let me tell you, it is worth every cent.
Even now when she has quiet days and I worry, I have a listen and can hear she is fine in there.