For a long time after my daughter was born, I wasn't sure if she could hear or not. I tried to get her to react / turn her head / wake up to voice, music, claps... Nothing.
One day I was taping up a box behind her and I pulled out a length of packing tape. It made that awful screeching noise and she was startled. It was a repeatable result. Her hearing was fine, she was just super chilled about noise in general. I found her limit with a roll of tape.
These days infants' hearing (including my own two childrens') are tested at birth, without them having to participate in the process at all (they can even be asleep)! https://www.audiology.org/consumers-and-patients/children-an...
Just where my mind went while reading the abstract. Babies hate this sound!
To them, it's like a baby crying.