Rayfield Byrd knows when it’s time to wake up every morning. The 68-year-old Oakland, Cal., resident hears a voice from the living room offering a cheery good morning. Except Byrd lives alone. A little after 8 a.m. each day, a small yellow robot named Mabu asks Byrd how he’s doing. Byrd has Type 2 diabetes and congestive heart failure, and about three years ago, he had surgery to implant a microvalve in his heart to keep his blood flowing properly.