I was looking for a trigger to end a cooperative mission: in this trigger i wanted to have ALL alive players in the perimeter of the trigger in order to launch the End of Mission; it was a sort of "Extraction" of the war zone.

So i made this (you will see few differences with STR part):
i created a BLUFOR player on a map (tested on Stratis in vanilla, and Sahrani through All In Arma Terrain Pack), i created a Flag in order to locate the Trigger, then i created a trigger, with a radius of 5m, i name it Trig1 (for the example) and set parameters as following:
Type: none
Activation: BLUFOR
Time: One Time (or repetition, it works too; and the trigger loops in "One Time")
Presence: "is present"
Condition: {(isPlayer _x) and (alive _x)} count playableUnits == {(isPlayer _x) and (alive _x)} count list Trig1;
On Act.: hint "test OK";
On Deact.: hint "test echec";
I've put an object (an oil puddle) out of the trigger zone to "see it"

When i launch Preview, the trigger is automatically activated, displaying "Test OK" on the top of the right of the screen. If a set "repetition" on the trigger and i step in the trigger zone, "Test echec" is displayed. {F24830}