Door Key Inverter

[Bucky]

Here's a device that, when the bottom door key is covered/uncovered continuously, will porduce the opposite effect out the top.  It's nowhere near as compact as I'd like, but it works.  It's also about as fast as a door key chain up the length of the construct.

gytobyl.

[Rene]

I have used a different device before, which works well if the door keys are horizontal, are the top one triggers the bottom one. Added to your device:
    fynatyg

[Bucky]

Here are a couple nice door key inverters for fast copy-adders:gevasab.  Note that the one on the left is bi-directional but defaults to left-to-right.

The nice thing about these inverters is that they work quite quickly.