There's a little-known feature of iOS called "sound recognition" that constantly listens and pops up an alert when it recognizes certain sounds that need attention, such as a crying baby, doorbell, or siren.

https://support.apple.com/guide/iphone/sound-recognition-iph...

I'm not deaf but I can imagine that being very useful.

There's of remote sign language interpretation and real time captioning services available. In the US, we have publicly funded video relay service (which translates between sign language and English for phone calls) and captioned calling (which provides captions for telephone calls). There are commercial equivalents of these services available for in person interactions and other countries.

Gallaudet, a college for Deaf students, even has videophone booths you can use for video relay service: https://createyourworldbook.com/wp-content/uploads/2018/06/d...

I don't know of any apps, but 20 years ago at least there were state run services for this. You call a number and someone will translate between your voice call and the ttd that the deaf use. (20 years ago a friend of mine worked for such a service, we have both moved on but I assume the service still exists)

It's a free government service in the US. 711 is the number for the relay service from TDD - voice. Unfortunately it is sometimes abused.