A mobile cart that holds a bag for receiving solid waste generated during a medical or surgical procedure. The cart includes a sensor that monitors whether or not an object containing metal is placed in the bag. A processor monitors the signal output by the sensor. If the sensor signal indicates that an object with a minimal amount of metal is placed in the bag, the processor momentarily asserts an audible alarm and continuously asserts a light alarm. The light alarm remains asserted until turned off. If, while the light alarm is on, the sensor signal indicates a second object with the minimal amount of waste is placed in the container, the processor again momentarily asserts the audible alarm. This provides notice that it may be necessary to investigate the contents of the bag to determine if not one but two or more objects were inadvertently discarded.