Spaceship Animation

I have a UFO hovering just over a hill, now what I'm trying to figure out is what if the best way to to have it take off when my FPS walker get within a cetain range?

I have a flight animation worked out already but I'm not sure how to code a script for this sort of thing, I thought about using a raycast but they are only directional and not omni directional, atleast I don't think they are??

But I want for the ship to take off no matter what direction the player appraches from. Any ideas on what to do for this??

I worked out a simple code using a sphere collider with a very wide radius but you can shoot at the collider which I don't want, also I can't seem to get my UFO takeoof sound to play when the animation starts for some reason, here is my code, it's pretty simple and I'm sure there must be a better way but I'm just not that great at code:

var UFOsound : AudioClip;

function OnTriggerEnter (col : Collider) {
    if (col.gameObject.tag == "Player") {
        animation.Play("UFOtakeoff");
        audio.PlayOneShot (UFOsound);
    }
}

Use Vector3.Distance.

here, just attatch it to your UFO:

var UFOsound : AudioClip;
var escapeDist = 20;
private var player : GameObject;

function Start(){
    player = GameObject.FindWithTag("Player");
}

function Update(){
    if(Vector3.Distance(transform.position, player.gameObject.transform.position) > escapeDist){
        animation.Play("UFOtakeoff");
        audio.PlayOneShot(UFOsound);
    }
}