Today's contractor grade programmable thermostats have built in A/C compressor protection for power outages, intelligent recovery so it is the temperature you desire at the time you set (instead of starting at that time), and even employ outdoor temperature sensors to automatically adjust the humidity level, protecting the windows, when outdoor temperatures fall below 30F. If these features are not of value to you at least get a cheap model at a local hardware store. Simply setting the temperature back 3-4 degrees for 8 hrs per day lowers the energy bills 10%. Remember, we get several repair calls each year from homeowners that did not install the thermostat properly. Turn the furnace switch off first and follow the instructions carefully!