Item Key Door

With this handy feature, you can force someone to drop any item into a hopper, and the door will then open. The button on the right shuts and locks the door until another item is dropped into the hopper.

In its default position, the door is closed. If you press the button on the right, nothing will happen yet. However, if you get an item and drop it into the hopper, then the door will open.

The hopper leads into a chest that is being measured by a comparator. Boosted by a repeater, the signal then powes the door, which opens it.

However, there is a hopper underneath the small chest that is being powered (so that it doesn't suck the items out of the chest) feeding into a large chest. This has a special relation to the button mentioned earlier.

When the button is pushed, it temporarily unpowers the second hopper, which then is able to suck the item from the small chest, which turns off the comparator, which then closes the door.

This can allow other players to give you an item every time they want to come in. It also allows you to show off your superior redstone skills!