This mod will be a few add on airlocks, mostly as surface attachable parts.

Over on the G+ community for KSP someone mentioned it would be nice to be able to add hatches to parts. That's a task I leave to someone who wants lots of coding headaches. However, and Airlock is quite fine. Basically a small part, with a crew capacity of one, with a hatch. I'll be adding in the MM config for Connected Living Space, so if you're using that, they'll be usable. For us non-realism type users, they are available to add hatch functions to any part.

Now, they're not hatches. You first need to transfer your kerbal to the airlock. Then EVA them. Repeating the process on the way back. This is both because KSP requires the hatch to be on the part that holds the EVAing kerbal. And because airlocks just work that way.

Now, initially, I'm making just one part, a mostly-replica of the ISS's Japanese Lab's Airlock, as it's about the smallest genuine airlock I could find.

Future plans;

Totally cheaty airlock/hatch. A REALLY small hatch that is impossibly small, for anyone who just wants to add a hatch, and is OK transferring Kerbals to wafer thin strange dimensions in limbo until they're EVAed.

A hatch and docking node set for any sizes that aren't completely ludicrous (I'm not sure if the small docking node is big enough for a sane looking hatch, haven't checked yet). So basically a part that's both a docking node and an airlock. I'll base at least one of those on the Common Berthing Mechanism. The part will be a bit longer than the existing docking nodes, but use the same widths for sizes 1, 2, and 3.