A filter condition indicator system is described herein. A pressure differential switch monitors air pressure across a filter, and a transmitter coupled to the pressure differential switch sends a signal to a networked device. If the pressure differential near the filter triggers the switch, then a “dirty” signal is sent to or retrieved by a mobile device which indicates that the filter is dirty and should be replaced. The filter condition indicator is able to be used by bypassing a thermostat and sending an alert to a computer or mobile device wirelessly. Alternatively, the filter condition indicator system described herein is able to be used in conjunction with a previously installed furnace/thermostat system by utilizing the pre-existing thermostat wiring. The filter condition indicator system is able to be used with HVAC systems, air conditioning systems, other heating/cooling systems, or other systems or devices.