Last Updated: Feb 1 2018.
Here’s an Escape from Tarkov guide for Keys that I got from UWS Gaming. I’ve modified it to include my thoughts on the key, or what they unlock. Those are in Orange.
Factory Key – This should never leave your gamma and opens two additional extracts and allows you to open the locked room in third floor offices. Possible weapon spawn in locked room, two coats, loose loot and occasional high end ammo. This key spawns in the office of 3-Storey in Customs, and the glass warehouse in Customs (in the blue locker or near the dead scav).
Currently the most expensive key. Selling for around 600-700K. Just to clarify what is written above, [...]