What do the alert codes 170, 173, 405, and 407 mean on my Honeywell thermostat?

Alert 170 indicates an Internal Memory Error requiring thermostat replacement. Alert 173 indicates a Temperature Sensor Error requiring replacement. Alert 405 is a Low Battery Alert (replace within two months). Alert 407 is a Critical Low Battery warning (replace as soon as possible). If you see a critical alert, you may not be able to access the home screen and should contact an HVAC professional.