Cell Key

Cell Key is a quest item in Pathologic. It is obtained in the Bachelor's route on Day 5 and is needed to free the Haruspex as part of the main quest "Vaccine".

The Bachelor will find the Haruspex imprisoned in one of the empty factories in the Works and several patrolmen guarding him. After getting rid of the guards, the Bachelor will find the Cell Key on one of the guards, which he can then use to open the cell door and free the Haruspex.

Quote
"This key was taken from one of the patrolmen guarding the imprisoned Ripper."