Mom's Locket is a trinket in The Binding of Isaac, added in the Afterbirth DLC.

Using a key to unlock a door, Locked Chest, or Key Block, will heal Isaac for half a red heart.

Converts all Half Hearts into Hearts. This works retroactively.

Also works for Keeper's coin hearts.

Will only work when a key is consumed from Isaac's inventory, meaning that having a Golden Key will not provide healing.

This page shows the latest information as of the new Repentance+ (Online Co-op) DLC.
To see information about this trinket for the previous Repentance version, check this page instead.

The following special synergies and interactions for Mom's Locket have been documented.

* Note that not all possible synergies and interactions are listed here.

Below is the Internal Item Description as shown in-game.
Note that some stat changes are not displayed here. Please see the main description for the full effects.

Mom's Locket

• Heal for 1/2 red heart whenever Isaac unlocks something
• Golden Trinket (without Mom's Box): Heal for 1 red heart whenever Isaac unlocks something
• Mom's Box: Heal for 1 red heart whenever Isaac unlocks something
• Mom's Box + Golden Trinket: Heal for 1 1/2 red heart whenever Isaac unlocks something
• Converts 1/2 red heart drops into whole red hearts

• Check out the trinket description on the external Isaac Wiki.