A push button for mounting on a shell includes a button body depressibly engaged in a through hole defined in the shell, a flexible circuit board, a rigid plate attaching to the shell and a conductive spring tab. The flexible circuit board is arranged between the a button body and the rigid plate. The flexible circuit board is brought into contact with the rigid plate. The flexible circuit board is electrically connected to a connector and includes a pair of normally-open contacts. The conductive spring tab is fixed to the flexible circuit board and aligned with the button body. The conductive spring tab is deformable. The button body is configured for being manually depressed so as to urge the conductive spring tab to deform and contact the pair of normally-open contacts, thereby generating a signal transmittable through the flexible circuit board to the connector.