The portable robot's name is Mabu, and at the recommendation of his health-care provider, she now lives with Mr. Byrd to help monitor his irregular heartbeat. She checks in on him two or three times a day to make sure he weighs himself, takes his medication and exercises regularly--and relays information back to his health team. "She's my little blue-eyed girlfriend," he says. "She keeps me on my toes." With the senior-citizen population expected to nearly double to 88 million by 2050 and some nursing programs stretched thin, researchers and elder-care centers are exploring the potential of digital companions, in robot or chatbot form, to help the elderly.