[Marttt]

Alex you can try to use "L4D_IsAnySurvivorInStartArea".
I usually use this stock above below but after a survivor leaves the saferoom, of course, after it leaves any "blocks" stop working.
Not the same thing you asked but similar.

Spoiler

/**
* Returns whether any survivor have left the safe area.
*
* @return True if any survivor have left safe area, false
* otherwise.
*/
stock bool:L4D_HasAnySurvivorLeftSafeArea()
{
new entity = L4D_GetResourceEntity();

if (entity == -1)
return false;

return bool:GetEntProp(entity, Prop_Send, "m_hasAnySurvivorLeftSafeArea", 1);
}