Play sound only ONCE

[machosalad]

I am using this script to play a sound when player collides with an area:

void OnStart()
{
AddEntityCollideCallback("Player", "Area1", "PlaySound1", false, 0);
}


void AreaSound1(string &in asParent, string &in asChild, int alState)
{
PlaySoundAtEntity("","amb_alert.snt", "mansion_1", 0, false);
}

However it plays the sound everytime the player enters or leaves the area! How do i make it play only once?