Variable e scope is the accumulate. You can't use it outside. But think about it for a second, when your rule is activated, variable e (if it would be possible to access it from the RHS) will have at least 6 different values. Which value do you want to use?
One possible (of many) solution could be to 'collect' all your events instead of counting them:
rule "Reset alarm"
when
a : Alarm()
c : Set( size > 5) from accumulate (
e : Event( level < 6) over window:time(10s) from entry-point "queue",
collectSet(e)
)
then
//All the Event objects matching the LHS are going to be in the set.
channels["reset"].send("Alarm resolved.");
end
Regards,