ok you'll need to create the buttons as seperate models, then position them on a keypad model in WED.
for each button, use String1 to store the number that is on the button.
To detect the actual clicking, you can use the EVENT_CLICK and run a function when the event is raised.
The function should get the String1 property (using entity.string1) and append it to a temp string (like my example). Finally check the string against the keypad models' String1 property. If they match, then open the door.