Baby Sleep Calmer for iOS

Plug power adapter into your device and run the app in "Listen for Cry" mode. Your phone will start monitoring the ambient sound volume in the room: if your newborn will make any loud noises, a soothing sound will start playing for 2 minutes (lullaby music, rain or hairdryer). After 2 minutes the app switches back to monitoring state.

You can also just play one of the sounds to calm your baby.