Trapped Chest

Trapped Chests are blocks which emit a redstone signal from all sides when opened, at a strength of one block per player using it up to 15 players. The Trapped Chest is characterized by a slight orange tint around the latch and a red line on the rim of the opened chest. Trapped Chests can be made into double Trapped Chests, and are able to be placed adjacent to normal chests without interfering, allowing two chests, or double chests, to be placed adjacent to each other. When you open one, a red shading will be visible around the chest inventory. These are great for making traps.

Usage
A trapped chest emits a redstone signal based on the number of players opening it (up to 15 players). You can also use them as traps or decoys, so they are useful if you don't want your goodies to be stolen. One way to hide the red stain around the latch is to put an item frame or a sign on the front of the chest. They are able to be placed adjacent to normal chests and store more stuff (not turning into a quad chest), so they are useful if you don't want to give up one block of spacing between chests and double chests.

They can also be useful to secret exits and doors (without using a door because they act like a lever). Basically, the trapped chest can be used as a second type of lever and third type of storage to the game. Since trapped chests emit redstone signals, you can place a dropper behind it and opening the chest can cause an item to be dropped in (see trivia). Like chests, they can't be placed adjacent to other trapped chests. You need one block spacing in order to place more trapped chests next to each other.

Trivia

 * Trapped chest is categorized as Decoration Blocks in the Creative Inventory although it emits redstone signal.