Not many people seem to realize that the most common dog breed for use as a service dog is the chihuahua. Anne Wicklund of Service Dog Registry notes that 70% of all service dog licenses are given for dogs smaller than a Yorkshire terrier.
Chihuahuas in particular are superior alert dogs for diabetes, high blood pressure, epilepsy, and to assist the hearing impaired, as well as therapy for depression. The working life of a skilled alert dog of the size of a labrador might be only five to eight years, as it can take two years for them to be fully trained, then they're too old for it before age ten. Chihuahuas, which are unusually long-lived, remain clear-headed little blighters until age fifteen or older!
An example is this little tongue-thruster Tiger, trained by a service dog charity organization to be a hearing dog for his first deaf owner Merthyr Tydfil.
After Merthyr's death, Tiger was repartnered partnered (in 2003) with Carol Hopkins, with whom Tiger's portrait above and at right was taken.
Carol and Tiger have been together for seven years. Before they came together, Carol had sunk into the depths of despair, as a music teacher who suddenly lost her hearing, then became confined to a wheelchair. Life seemed no longer worthwhile. Tiger, though one of the smallest of small dogs ever trained for the deaf, was a huge bundle of personality, and Carol's gloom lifted entirely in the little fellow's company!
Though well trained to enthusiastically alert Carol to household sounds, he turned out to be even more watchful of her health than expected. Shortly after they first came together, she had a choking reflux episode in her sleep which could've killed her. But she woke suddenly with Tiger scrabbling around her head and licking her face continuously to wake her up and get her breathing again.
On another occasion when Carol had fallen from her wheelchair and couldn't move, Tiger ran for a caretaker outside in the garden. When the paramedics arrived, they had to lift Tiger off her, as he wanted to stay right on her the whole time, comforting Carol. She says of him, "I¼m very proud and privileged to have Tiger. He is a little bundle of fluff who has changed my life. I think the world of Tiger and couldn't imagine life without him. If I didn¼t have Tiger with me, I really don't think I would have the will to live."