You could have the bell cast a spell - give the spell's magic effect a fairly large area and add a script to the magic effect like the below (Skyrim example, should still work)
Scriptname _StopCombatExample extends ActiveMagicEffect
Event OnEffectApply(Actor akTarget, Actor akCaster)
AkTarget.StopCombatAlarm()
EndEventIn order to prevent it from messing with any passing raiders, turrets, etc. you can add some GetInFaction conditions to the magic effect.