When a baby is newborn they will often startle. That's how you now they can hear ok. Does your baby startle? As they get a little older, they should start responding to your voice.
Usually when the child is born, the hospital will do a newborn hearing test. They usually write that on your discharge papers, it will say (newborn hearing test). And it will say : PASS or Needs further screening.
If you would like to do your own test, get something crinkly, and have it make a sound, out of the child's line of vision. If he/she doesn't acknowledge the sound, see a doctor.
The Baby begins to hear their surrounding from the time they were in the womb. They can hear the Mother's heartbeat and external voices, such as his family members. Once the baby is born, the begin to exercise one of eight reflexes, such as Babinksi, Moro, Palmar, etc. During the Moro Reflex, the infant begins to respond to unexpected loud noise by startling if the infant hears a bark or the sound of the vacuum cleaner. They are four distinct ways to find out if your newborn is able to hear normally; they startle, spread out their arms, un-spreading of arms, and most importantly crying. Pay attention to how closely your baby listens when you are talking to them in a calm and soothing voice.