How is that type of key and switch part called? Googling "Safety key" does not yield anything related :(

This is a dual contact switch that emulates what Estes has used in their handheld launch controllers for over a half-century.  It consists of a custom circuit board and two AAA battery spring contacts.  To engage the switch, you insert an Estes safety key, which shorts the connection between the two contacts.  Once I get the instructions written, you will see a picture of the safety key switch assembly.  I will also include on this project page a link to the custom circuit boards required for this launch controller.

I built something similar, but using a capacitor discharge when I flew rockets as a teenager. I built it into an AMT tricorder model as the case because nerd. I like both the look and the feature set of this launch controller.