A tilt switch includes a base and a cover body. The base includes an upright support having a lower groove, and first and second lower passage holes communicated with the lower groove. An emitter is mounted on the base to emit a light signal. A receiver is disposed opposite to the emitter to receive the light signal. The cover body includes first and second press pieces respectively having first and second upper passage holes that complement with the respective first and second lower passage holes to define first and second light passages, respectively, and an upper groove cooperating with the lower groove to define a chamber. The light signal propagates along a light path passing through the chamber from the first to the second light passage. A ball member is rollable within the chamber to block or unblock the light path.