I've worked with deaf dogs.
I've also volunteered with service dogs.
Hearing dogs or signal alert dogs are dogs that are trained to alert handlers to sounds in their environment. That could be - baby crying, phone ringing, doorbell/knock etc, someone calling out for them. I realize that light flasher and other things often alert people in the same way; I'm just saying what the dog's job is.
The dog is trained to check out the source of noise and alert the handler, and/or try to entice the handler to follow dog to the noise. Service dogs in general, of which hearing dogs are one kind, are often taught a general "get help" cue, that means the dog is supposed to go find another person in the home, or in the vicinity if the handler is out and about, and try and get the second person to come with them to see what is needed. This is useful if, for example, a person with a mobility dog has fallen out of their chair and for whatever reason can't get back in it. A hearing dog can also get help for other household members..if say there's a kid in the house who gets hurt and calls out for someone...the dog can be trained to alert the handler/parent to the fact that a child is calling for them. <again, just describing the possible jobs for the dog>
I didn't see where the article mentioned the hearing alert dogs actually being deaf...