button_keypad is a prefab located in the
Prefabs HL2 folder, containing a keypad setup.
This prefab is comprised of two entities
When pressed, the
func_button is configured to make a specific sound and make the model briefly display "
*ERROR*" message on the readout portion of skin.
func_button, adjusting the skin property to be switched to "1" instead of "2", and adding an output to another entity, you can easily have the keypad grant access to something instead.