What do the alert codes mean on my Honeywell thermostat?

The thermostat displays several alert codes: 170 indicates an internal memory error requiring thermostat replacement; 173 indicates a temperature sensor error requiring replacement; 405 is a low battery alert meaning batteries should be replaced within two months; 407 is a critical low battery alert requiring immediate replacement. Critical alerts may prevent access to the home screen, and you should call an HVAC professional if you cannot resolve them.