How do I lock the thermostat keypad to prevent unauthorized changes?

Go to Installer Setup Number 0670 in the Advanced Settings Menu and select option 1 for a partially locked keypad or option 2 for a fully locked keypad. A partially locked keypad allows only the temperature up and down keys and access to Installer Setup mode, while a fully locked keypad allows only access to Installer Setup mode. The factory default is 0 (unlocked), which makes all functions available. (Page 17)