How do I lock the keypad on my T4 Pro thermostat?
Press Menu, navigate to LOCK using the arrow buttons, then press Select. Choose OFF (unlocked), PART (partial lockout allowing only temperature changes), or ON (no access allowed). To unlock, press the center button and enter the default password '1234' using the arrow buttons and Select to advance through each digit.
From the official Honeywell T4 Pro Thermostat manual, page 5
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