Gizmos.DrawWireSphere  

var explosionRadius = 5.0;
function OnDrawGizmosSelected () {
// Display the explosion radius when selected
Gizmos.color = Color.white;
Gizmos.DrawWireSphere (transform.position, explosionRadius);
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
public float explosionRadius = 5.0F;
void OnDrawGizmosSelected() {
Gizmos.color = Color.white;
Gizmos.DrawWireSphere(transform.position, explosionRadius);
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

public explosionRadius as single = 5.0F

def OnDrawGizmosSelected():
Gizmos.color = Color.white
Gizmos.DrawWireSphere(transform.position, explosionRadius)