To open a hatch in DBD, you need a key. Just like hatches, keys spawn at random, so you will have to make a run around the map to find it. Optionally, you can acquire one before the start of the match. There are two key types – the Dull Key, which only lasts for five seconds, and the Skeleton Key, which can be used for 30 seconds. The Plunderer’s perk raises your odds to find a key.