The Velocity door system includes 4 door safety latching pins that lock into receivers on the fuselage. When latched, the door becomes a very strong reinforced section of the fuselage, as both the door and the fuselage have carbon beams that when connected become a very stiff structure. A safety latch drops behind a latching rod when fully inserted, and must be manually lifted separate from the door lever to unlatch the pins. This safety feature has an emergency escape feature that includes a pin that extends through the door so that rescue workers can unlatch the pilot side pins from outside of the airplane. Many builders (and most factory aircraft) include a microswitch to verify that the pins are fully inserted. On my aircraft (N44VF) I elected to not sense the door pin position, but rather that the safety latch is fully down and locked. My warning lamp requires both door safety latches to be fully down and locked for the warning lamp to be extinguished.
Here is a picture of the installation of my safety latch and door locking mechanism. Note that the door lock uses the same latching bar. On top of the U channel aluminum block is a pin that extends forward through the door so that the security latch can be released from outside the plane. This feature is only present on the pilot side door. You can see that the switch is actually checking that the safety has come down and locked.
This installation technique requires that wiring come from the door to the fuselage, which is why the factory doesn't do it. I drilled a hole near the hinge, added a grommet, and then siliconed the wire in place to prevent (hopefully) air and water leaks.
Here is a shot of the door safety latch installation from the builder's manual. You can see the exterior lift tab as well as the roll pin, springs, etc.
Here is a shot of the door pin receiver installation from the builder's manual.
Here you can see my annunciator panel in press-to-test mode. The middle red light on the top row is the "Door Open" alarm. Yellow lamps are cautionary, red are serious warning conditions.
