How do I lock the keypad to prevent unauthorized changes?
Press Menu, navigate to LOCK, and select either PART (partial lockout allowing only temperature changes) or ON (no access allowed). To unlock, press the center button and enter the password '1234' using the navigation buttons, pressing Select after each digit.
From the official Honeywell T4 Pro Programmable Thermostat (TH4110U2005/U) manual, page 5
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