A filter includes filter medium that screens out impurities from a fluid, and a conductive thread contacting the filter medium. A power source provides electric current flowing through the conductive thread, which causes electrical phenomena that is detected by a sensor. A sensor detects the electrical phenomena resulting from the flow of electric current through the conductive thread. Buildup on impurities in the filter causes a change in the electrical phenomena, which change is detected by the sensor and indicates the level of impurities in the filter. An indicator is in communication with the sensor, and provides an alert that the filter should be replaced when the level of impurities exceeds a predetermined threshold.