An under-sink disposal unit includes a motor, a disposal chamber, and a disposal throat. The disposal throat extends from the disposal chamber to an opening in a top of the disposal unit and defines a passageway through which objects pass into the disposal chamber for grinding. The disposal unit further includes a coil assembly including an arrangement of coils. The arrangement of coils is used to detect the passing of a metallic object in the passageway through the disposal throat. Furthermore, the arrangement of coils includes at least one coil having a loop that is oriented with respect to an axis of the passageway through the disposal throat such that objects passing through the disposal throat into the disposal chamber pass by and proximate to, but do not pass through, such loop. Preferably DC injection braking is used to stop the motor upon detection of a metallic object.