This is an image of the door https://i.imgur.com/IIhWNF4.png
The blocks on the door slide left and right. If the blocks in the middle stack up as brick, stone, brick and you press the button on the left then the door will open.
You should know that this door isn't super fast or compressed.
Mediafire link: http://www.mediafire.com/download/hb6q4v3cdb6cfzd/3x3_lock_with_door.7z
I know this might not be as impressive as the games people have built or computer using redstone, but its kinda cool and i spent a while on it
Here is a video: