Lt. Jeff Nightengale told reporters the 48-year-old woman was arrested Monday at the Garden Grove Medical Center after a hospital staffer stopped her from leaving with the baby. Garden Grove is near Anaheim, in Orange County.
Police say the suspect posed as a nurse and told the baby's mother to take a shower. She then put the newborn in a duffel bag and tried to carry her out, but a monitoring device on the baby triggered an alarm.
Nightengale credits an alert employee and hospital policies for stopping the suspect and saving the baby.
The child was unharmed and is back in her mother's care.