What about bedrooms with no roof? Or floor grates, and everyone else walks around on top?
Well, that won't affect the pathfinding, so it doesn't really impact on the effectiveness of the design. Unless you mean that that would allow detection of when the vampire feeds, in which case it's not something that the design addresses - we're looking for prevent vampire feeding, not detecting it.
Needs an inverter too-- floodgates and doors allow passage on an open signal, disallow on a close. In fact, really, you want to use all doors, no floodgates, to eliminate floodgate latency.
My bad, I got confused for which direction that the doors work when in a mechanism. In that case, we need to replace the doors with something that is open when deactivated and closed when activated. The only possibilities that I can think of off the top of my head are to either use a retracting bridge (which has latency issues) or to use a NOT gate and a door (which requires more of an investment). Though latency should only be an issue when the inner room is small and the path is therefore short.
If dwarves bump into each other in the hallway, they might take corner squares, so that can screw it up when children are involved, but the risk is low.
That's why all the hallways involved are one tile wide, and away from traffic from anyone that doesn't want to get into the room anyway. Even if the dwarf takes a corner square on the corner, when they travel down the passage they'll trigger the pressure plate anyway.
The real risk is that of your bed being used for something other than sleeping. A dwarf might start the suffering the effects of a syndrome only after making it to bed-- such a dwarf would be a goner. Any dwarf dying in bed (perhaps just old age) would tie up burial dwarves in infinite loops until you dismantled the room.
That's a problem with any automated airlock system. In that case, all would happen is that you would get one less idler for as long as it took for you to notice what's going on. I suppose with more research into sleep durations and timers, it should be possible to have it automatically close when the dwarf goes in and open a short while after the dwarf wakes up.
But you could design the second path like this: Hatch-Plate-Hatch. The Plate activates the hatches, trapping anyone on them. Then you can flush them down.
Or you can build the second path with a long retracting bridge with a one level drop below, and hook it up to the pressure plate.
You can trap the vampires this way, and i think it would work with multiple vampires too.
That would work in the sense that it would trap any potential vampires, but it would also trap any non-vampire dwarves that try to get into that room for any reason (e.g. haulers, children, etc) and they would starve to death unless you found them.
I'll work on some alternate designs and have them up in a bit.