A mobile wireless device (e.g. smart phone) may be used to remotely control an HVAC system. A program code stored in the memory of the mobile wireless device may cause the mobile wireless device to store geographic information in the memory of the mobile wireless device, monitor a location of the mobile wireless device, and compare the stored geographic information to the location of the mobile wireless device. If the comparison meets predetermined criteria, the program code may cause the mobile wireless device to transmit a command either directly or indirectly to an HVAC controller, causing the HVAC controller to transition from a first operating state having a first temperature setpoint to a second operating state having a second temperature setpoint.