In short

Keycard Cottage No. 3 is a keycard for the building “Cottage No. 3” in Loraine Hills. It opens: locked room. Behind the door: 2 large safes, 3 cabinets, 1 computer · Powder, Brick, Cash. The key fits only this place.

KeyBuildingDistrictOpens
Keycard Cottage No. 3Cottage No. 3Loraine HillsLocked room

Where it is

The building is on the interactive map. All keys, doors and safes of the city: Locked doors, Safes and containers, the key guide.

The game data does not list where this key drops or is sold, so we do not guess.