I bought this when I was about 20 weeks pregnant with twins, figuring that with two of them in there Id be more likely to hear something. I could easily find my own heartbeat, so I know the app works, but finding the babies heartbeats is much more difficult. They are smaller and so are their hearts, and a number of factors can make it difficult to find the beat: location of the placenta, position of the baby, placement of your organs, digestive activity, etc. So if you cant find your babys heartbeat easily, dont freak out like something is wrong with your pregnancy or think the app is broken. It just takes time to get the hang of it, and even then you may not always find what youre looking for.
What this app IS really good at is recording the sounds of my babies movement. I am now 27 weeks pregnant (7 months) and I can hear every little kick, punch, and wiggle, which sounds like muffled scuffling on the audio. Kind of fun to see and hear that theyre moving so much more than I can feel!
Bottom line: The app works, but its no medical device. Its not going to always find a heartbeat, but it will let you hear movement and is a fun way to get to know your little one a bit before the baby is born.
One request: It would be nice to have the ability to custom label the recordings. With twins, Id like to be able to write which audio belongs to which baby.