02/10/2010 at 08:27 AM EST
There was something special about the look on Wyatt Earp's face five years ago when Don Callahan, 72, adopted him at a fair held for homeless pets at the Detroit Zoo.
"He seemed to look at me with love in his eyes, plus I saw he got along with a cat that was also there," Callahan tells PEOPLEPets.com about his beloved mixed breed Airedale, now 6 years old. "I already had a cat and was happy to see they would get along. So I took him home, and he has become my best friend."
The 75-lb. dog had the chance to prove his love for Callahan last month when the retired police officer and canine handler, who is a diabetic, collapsed during one of their twice-daily walks around their hometown of Royal Oak, Mich.
It was pitch black outside and no one could see Callahan lying on the ground. Wyatt Earp stood by his side barking as loudly as possible.
Finally, a woman living across the street looked out the window. She thought she saw a duffle bag near the pup (it was actually Callahan) and only called the police to report an annoying dog.
"When the police arrived, Wyatt Earp wouldn't let the officer near me," Callahan was told later. "But when the fire rescue came to give me a shot of glucose, they tied him to a tree, and he seemed relieved that I was being attended."
Callahan's memory of the event is hazy: He remembers reaching out for a wall at a local condominium, but the next thing he knew it was a day later and he was in intensive care at a hospital.
His blood sugar level was only 18 when the emergency staff found him (anywhere between 70 and 120 is normal). The senior has an implanted glucose monitor to help regulate his sugar levels, but the sensor failed that night because Callahan, who lives alone on a fixed income of $1,200 a month, could not afford the $75 a week replacement cost.
"I was told that if 20 to 30 more minutes had gone by, I would have been a dead man," he tells PEOPLEPets.com. "I owe my life to Wyatt Earp. He is my buddy. I love him as much as I love my kids." See more amazing pets on PEOPLEPets.com:Paralyzed Rabbit Eases Therapy for Hospitalized Children Goggles On, Dog Is a Dirt Bike Speed Racer