You could simply use "SMART_ACTION_CALL_FOR_HELP" funcion of smart_scripts in database (http://collab.kpsn.org/display/tc/smart_scripts). It'll cause an NPC to call for help any other NPCs of same family type (http://collab.kpsn.org/display/tc/creature_template) in X (set by urself - works even for such high values like 200+) yards radious. You're also able to hide "[NPC name] call for help" massage on the chat in smarts.
Remember to set both NPCs with smart_scripts (logical, isnt it?) and fit "SmartAI" under AIName in "creatures_template" table, to make em work.
Works well to me under 4.3.4 core.
Also don't act like disabled - smarts are easy with wiki support.
gl and greetings,
Memorabilis.