UPDATE, Sunday: He was found safe.
Boston Police have mounted an extensive search for Derrick Livingston, who has Alzheimer's and who was last seen around 9:30 a.m. at 151 Glenwood Ave. in Hyde Park.
Livingston, 74, wears a white tracking bracelet. Earlier today, police - and a State Police helicopter - swarmed the area of the Fenway and the Longwood Medical Area when an officer picked up a signal from the device.
He is wearing green pants and a burgundy plaid shirt. He may be carrying a black Coach bag or Macy's shopping bag with men's clothes in it. Police say he used to work in the area of Huntington and Mass. avenues and used to live in the area of St. Botolph St.
If you see him, contact E-18 detectives at 617-343-5607.