Thermostats where the landlord can set a minimum temperature for heat?

[Kimberly T.]

We recently bought a 4plex in Colorado (yea!).  Our other rentals are in Orange County CA and Scottsdale AZ, so we've never had to worry about pipes freezing/bursting.  I have heard of thermostats that you can install that have a minimum temperature setting (say, 50 or 55 degrees F) to automatically turn on the heat even if the tenant doesn't have the heater on, and we'd like to put those in to prevent frozen pipes.  Where can you buy those?  Home Depot/Lowes?  How do you find them among all the thermostats available?  Do they have a specific name?  Sorry, this is new to me.