Unity Trigger Setup

When user enters a region, activate certain events.

First is using a simple physics collider. Setup BOX Collider or Sphere Collider component on the target object. provide a tag for it, this case called "ball". Do remember to set the isTrigger active on the object too.

Add onTriggerEnter function to the movementControl script:

using UnityEngine;
using System.Collections;

public class movementControl : MonoBehaviour {

    public float moveSpeed = 10f;

    // Use this for initialization
    void Start () {

    }

    // Update is called once per frame
    void Update () {
        if(Input.GetKey(KeyCode.UpArrow))
            transform.Translate(Vector3.forward * moveSpeed * Time.deltaTime);

        if(Input.GetKey(KeyCode.DownArrow))
            transform.Translate(Vector3.back * moveSpeed * Time.deltaTime);

        if(Input.GetKey(KeyCode.LeftArrow))
            transform.Translate(Vector3.left * moveSpeed * Time.deltaTime);

        if(Input.GetKey(KeyCode.RightArrow))
            transform.Translate(Vector3.right * moveSpeed * Time.deltaTime);
    }

    void OnTriggerEnter(Collider other) 
    {
        if (other.gameObject.CompareTag ("ball"))
        {
            other.gameObject.SetActive (false);
        }
    }
}

another example is to create a trigger region and set it active when user enters the region:

using UnityEngine;
using System.Collections;

public class triggerEnter : MonoBehaviour {

    // Use this for initialization
    void Start () {

    }

    // Update is called once per frame
    void Update () {

    }

    void OnTriggerEnter(Collider other) 
    {
        if (other.gameObject.CompareTag ("Player"))
        {
            transform.localScale += new Vector3(3f,3f,3f);
        }
    }

}