Trigger

using UnityEngine;

// Attach this to a Coin with a Collider that has isTrigger = true
public class CoinPickup : MonoBehaviour
{
  public int value = 10;
  public AudioClip pickupSound;

  void OnTriggerEnter(Collider other)
  {
      // Only react to the Player
      if (!other.CompareTag("Player")) return;

      // Award points via GameManager
      GameManager.instance.AddScore(value);

      // Play a pickup sound
      AudioSource.PlayClipAtPoint(pickupSound, transform.position);

      // Remove the coin from the scene
      Destroy(gameObject);
  }
}

using UnityEngine;
using System.Collections;

// A fire zone that damages while you stand in the trigger
public class DamageZone : MonoBehaviour
{
  public float damagePerSecond = 10f;
  public LayerMask damageable;

  Coroutine damageRoutine;
  PlayerHealth currentTarget;

  void OnTriggerEnter(Collider other)
  {
      if ((damageable.value & (1 << other.gameObject.layer)) == 0) return;

      currentTarget = other.GetComponent<PlayerHealth>();
      if (currentTarget != null)
          damageRoutine = StartCoroutine(DamageLoop());
  }

  void OnTriggerExit(Collider other)
  {
      if (damageRoutine != null)
      {
          StopCoroutine(damageRoutine);
          damageRoutine = null;
          currentTarget = null;
      }
  }

  IEnumerator DamageLoop()
  {
      while (true)
      {
          currentTarget.TakeDamage(damagePerSecond * Time.deltaTime);
          yield return null; // Wait one frame
      }
  }
}