The Caregiver is an employee of Casa Tranquila. She interpreted Hector "Tio" Salamanca's bell ringing by getting him to select a row and then an character from a chart of letters and numbers.
History
Season 4
After Walter White has gotten Hector to agree to his plan to kill Gustavo Fring, Hector asks the Caregiver for the DEA by spelling out "Need DEA".
When at the DEA office, Hector demanded to speak with Hank Schrader. Once Hank arrived, Hector spelled out "S-U-C-K-M-Y" and "F-U-C-" before Hank called the meeting off and sent Hector back to the nursing home. The Caregiver apologized profusely for Hector's behavior. ("Face Off")