The Honeywell CG511A thermostat guard is available at The Home Depot and Amazon.com. The guard fits Honeywell and most other thermostat, protecting them from tampering or damage. The CG511A has a clear plastic cover and key lock. This thermostat guard measure 6.5 inches by 7.5 inches, with a 3-inch depth.
The Honeywell CG511A thermostat guard is molded from polystyrene, has an open back for easy installation and fits thermostats measuring 5.1 inches by 6.1 inches. The CG511A costs approximately $18, as of March 2015.
The Home Depot also sells a slightly larger thermostat protector, manufactured by Safety Technology International. The STI-9110 measures 7.56 inches by 9.5 inches, with a 3.9-inch depth. This polycarbonate thermostat also has a key lock and ventilation slots for air circulation. The STI-9110 sells for roughly $25.