First appearance: Welcome to Lovecraft #2
Use: Create a living echo
The Echo Key was created by Benjamin Locke, in June 1775. Benjamin seemed to not know what function the key would have, and described in his journal that entering the Wellhouse, he was asked who he sought. When he said Joshua’s name and he appeared, Benjamin fled.
The Echo Key is used to summon a tangible “echo” of a dead person to the Wellhouse. Entering the Wellhouse, the user is asked “Who?” Saying the name of someone summons their soul as a tangible Echo that rises from the well.
The Echo is trapped in the Wellhouse, as attempting to leave through the door results in the Echo fading away. The Echo can only leave the Wellhouse through use of the Anywhere Key, where they technically aren’t walking through the Wellhouse door.
Chamberlin Locke speculated that an Echo “longs for the warmth and comfort of “That Other Place”, and that using the Echo Key is selfish. Ellie Whedon also believed that Echoes are at peace, and therefore struggle to understand complex human emotion.
Source: Locke & Key Wikia