Hi,
I'm new to the forum and new to GECK.
I've been trying to make my own Perception mod (like the one from 'Mart Mutants' only without the other 133MB). The idea is to create global effect that would affect all NPCs not wearing power armor between certain hours. Unfortunately I'm not very good at scripting at all and even getting past the beginner's guide does my head in. Anyway, my idea of the structure of this mod is that I need a single spell and a script to activate it. Perhaps there is more to is but as I said I don't really understand scripts.
I came up with something like that:

scn PerceptionReductionScript

begin GameMode

if (object is an NPC)
_if (time is between 2200 and 0800)
__if (NPC is wearing power helmet)
___addspell PerceptionReductionSpell
__endif
_else
__removespell PerceptionReductionSpell
_endif
endif

end

Well, I'm not sure how to activate the script in the game. What would trigger this script if it's GameMode? Should it be GameMode?
I'd appreciate any help.
Thanks
Kris

Is there any tutorial that would show how to write a simple mod *from a scratch*, please?

What you ask for is a bit complicated for a beginner to accomplish. My best answer would be to use http://fose.silverlock.org/fose_command_doc.html to perform a "ref-walk" at fixed intervals and adjust your NPCs perception accordingly. A ref-walk is performed by using FOSE's GetFirstRef, GetNextRef, Label and Goto commands. There is a http://geck.gamesas.com/index.php/Main_Page.