The Pharros' Lockstone can be fit into Pharros' Contraptions found throughout the game. They can either activate a trap or reveal the location of a secret passage which would not be accessible otherwise. They can also activate processes which aren't helpful or detrimental to the player.
- The Explorer class starts with one Pharros' Lockstone.
- One can be purchased from Merchant Hag Melentia for 4,000 souls.
- One can be found in the library, in the mansion unlocked by the House Key in Majula.
- One can be found in the pit in Majula, after buying the shortest ladder from Laddersmith Gilligan. The player will still require the Silvercat Ring to survive the fall.
- One can be found in a cell at the bottom of Sinner's Rise.
- One can be found on the body across a chasm from the bonfire in Huntsman's Copse. The same body also has a Token of Fidelity.
- One can be found on a ledge on the Earthen Peak next to a piece of Twinkling Titanite. Either drop down to it, or pay Laddersmith Gilligan 2000 souls.
- One can be found by dropping down the hole after the Royal Rat Vanguard boss fight.
- One can be found in the Iron Keep, up a set of stairs near to Magerold of Lanafir.
- One can be acquired by severing Rotten's arm, but it's not a guaranteed drop.
- If the player is part of the Rat King Covenant and is successful in defeating a trespasser in the Grave of Saints or the Doors of Pharros, they will receive a Pharros' Lockstone, along with a Rat Tail, for every victory.
- Also, if the player gets summoned as a grey spirit by a member of the rat king covenant, they will gain a Pharros' Lockstone if they kill the host.
- Drops from the small Dog Rats in Doors of Pharros, as well as the Royal Rat Authority boss room.