My very good friend Big Dog and I are naturally going to disagree--but not being primitives, it doesn't affect our liking for each other--because of wholly-different life experiences, but a dog can be of invaluable service to a deaf person.
A dog can be trained to sense that its owner can't hear, and that its job is to alert its owner when the dog hears some noise the dog interprets as indicating something or someone dangerous.
You're describing it perfectly, and I agree 100%. A Hearing Dog is trained to alert the handler to specific sounds- that is the Hearing Dog's "task" that is required of qualified Service Dogs under the ADA. Velvet's job is to hear things I can't, to alert me to certain sounds, and to show me the source of sounds.
Velvet is trained to warn me about smoke detectors, ringing telephone, car horns, sirens, doorbells, knocking (as on a door), gunfire, and the beeping on my stove. A handler or trainer can add new sounds as needed- I added the sounds of my cell phone and gunfire to her
repertoire. Some dogs are trained to alert to crying babies or boiling water.
One of the consequences of being deaf is that one isn't aware of what's behind one, or on either side of one; only what's in front of one. Hearing people might hear a noise or something, and turn around to look, but I of course hear no noise.
The hippywife primitive Mrs. Alfred Packer's hippyhubby Wild Bill could be noisily trampling around inside this house right now, and I'd be the last person to know it (unless, of course, he was right in front of me). He could come up to me from behind and garrote me, and I'd never know what happened.
Big Dog might have some other uses for a service dog, but that's what I consider the essential purpose of them; to warn one that danger might be in the offing. I can't think of any other purpose, but perhaps he can.
A hearing dog also notices everything in the handler's environment that moves or makes noise. In Velvet's case, she raises her ears and points her nose toward sound and movement sources- which is something I need due to the nature of my hearing loss. I keep her in my field of vision, and I look at whatever she is responding to.
Currently, my situation is that there's five cats here, who came with the place, who seem to "understand" that I can't hear, and raise a ruckus when they sense that something isn't kosher, and want to alert me about it. They're very good at it, but alas I don't give them as much credence as I would a dog (since cats aren't as bright as dogs).
