A security device in an electronic device which protects against unauthorized disassembly includes light sources, a plurality of photosensitive elements, a detection unit, a storage unit, a processor, and light guiding devices. Light conducting channels are provided between the light sources and the induction elements. Barrier objects that block light are installed at certain first light guiding channels of the light guiding channels, and are removed from the first light conducting channels when the electronic device is disassembled, so that induction signals output by the photosensitive elements are changed from the model or original digitally-recorded signals.