Animation play in reverse OnTriggerExit

I have animated a needle to go one way and stop when entering a collision box, now i would like it to reverse back to its normal state and stop again

when the player exits the collision box is there anyway of doing this?

#pragma strict

var AnimateNeedle : AnimationClip;

function Start ()

function OnTriggerEnter () 

function OnTriggerExit() 


You can reverse animations using the speed value.

Animator anim;

anim.speed = -1;//play animation reversed
anim.speed = 1; // play animation normal