Redstone Locks Trapped Chests

While a Trapped Chests gets a Redstone Signal from a Repeater going directly into it, the items inside the Trapped Chest cannot be removed, you can still open the chest and take a look at the items but you can't add or remove anything until the signal is turned off.

You can already lock repeaters with other repeaters like this but doing it for a Trapped Chest would make it easier to make shops on servers and also give the Trapped Chest another use.