| Desktop-Only Content: This information (or parts of it) applies only to the desktop version of Terraria.
Placed Gem Locks, in both their on and off states.
A Gem Lock is a special mechanism which acts as a container or altar for a Large Gem. A Gem Lock will emit an activation signal if the corresponding Large Gem is placed inside it and once again if it gets removed. This allows for a simple contraption that uses only one mechanism to keep something like a door open as long as the gem is inside the lock because if it gets taken out it will immediately close.
- The Gem Lock is the only craftable mechanism that emits a signal, while not having wire in the recipe.
- Painting the Gem Lock will affect the color of the gem placed inside it.
- The Gem Lock only sells for 1 Silver Coin, despite the ingredients being worth more.