I have a Doppler so I can listen to the baby's heart when I get scared that it's all going to shit (which is much less often than it used to be). I use it maybe once a week. When I was pregnant with Piccolina I used the it almost every night. As the day progressed I would get more and more panicked that something happened. The sound of her heartbeat relaxed me enough so I could get to sleep. It made me giggle with happiness and I would delight in the unbelievable fact that I had a real live person growing inside of me.
Piccolinna loves to help Mamma with her "medicina" (medicine in Italian...that's what we call the doppler). She loves to help Mamma by pushing the button to turn the doppler on and she nods as I tell her, "That's baby's heart". Inevitably she wants to hear her own heart. So I put the doppler on her chest and she giggles with delight at the sound of her heart beating. Just as I did three years ago.