A system for detecting disposal of metallic objects into an opening of a medical waste container, including: an indicator for indicating passage of metallic objects through the opening, a pair of receive coils and a transmit coil spaced therebetween shaped for receiving waste therethrough adjacent to the opening, and a controller in electrical communication with the coils. The controller generates and communicates a transmit signal to the transmit coil, which generates a magnetic field that induces voltage in each of the receive coils, which each generate a receive signal. The controller generates a waveform based on the receive signals with a baseline corresponding to absence of metallic objects, and analyzes the waveform with respect to opposite first and second thresholds. The controller activates the indicator in response to metallic objects passing through the coils when the waveform first exceeds the first threshold and then subsequently exceeds the second threshold.