How do I lock or unlock the thermostat screen to prevent tampering?

Access the screen lock feature through advanced function 0670 on page 25, where you can select three options: 0 (fully unlocked), 1 (all functions locked except temperature controls and CANCEL key), or 2 (fully locked with no keys functioning). When partially locked, pressing a locked key displays 'SCREEN LOCKED' for several seconds; you can unlock by pressing any unlocked key during this time.