A method for detecting tramp material in an inertia cone crusher having an outer crushing shell and an inner crushing shell is provided. The inner crushing shell is supported on a crushing head. The crushing head is rotatably connected to an unbalance bushing. The unbalance bushing has an unbalance weight for tilting the unbalance bushing when it is rotated, such that the crushing head will gyrate about a gyration axis, the inner crushing shell thereby approaching the outer crushing shell for crushing material in the crushing chamber formed therebetween. The method includes the steps of measuring at least one of a position and a motion of the crushing head; obtaining, based on the measurement, a gyration value; comparing the gyration value with a gyration reference value; and determining, based on the comparison, whether to issue a tramp material warning signal indicating the presence of tramp material in the crusher.