Unity tap button (wth SpriteRenderer and BoxCollider2d) - I'm using this a lot.

CustomTapBehaviour

using UnityEngine;
using System.Collections;

[RequireComponent(typeof(BoxCollider2D))]
public class CustomTapBehaviour : MonoBehaviour
{

    #region Fields
    public delegate void HandlingEv(GameObject invoker);
    public event HandlingEv OnHandlingEv;
    #endregion

    void Update()
    {
        if (this.GetComponent<BoxCollider2D>().enabled)
        {
            for (int i = 0; i < Input.touches.Length; i++)
            {
                if (Input.touches[i].phase == TouchPhase.Began)
                {
                    Vector3 wp = Camera.main.ScreenToWorldPoint(Input.touches[i].position);
                    Vector2 touchPos = new Vector2(wp.x, wp.y);
                    if (collider2D == Physics2D.OverlapPoint(touchPos))
                    {
                        this.TriggerEv();
                    }
                }
            }
        }
    }

    void OnMouseDown()
    {
#if UNITY_EDITOR
        if (this.GetComponent<BoxCollider2D>().enabled)
        {
            this.TriggerEv();
        }
#endif
    }


    private void TriggerEv()
    {
        if (this.OnHandlingEv != null)
        {
            this.OnHandlingEv(this.gameObject);
        }
    }

    internal void ClearListeners()
    {
        this.OnHandlingEv = null;
    }
}