3D triggers not detecting rigidbody

I'm just trying to build a simple trigger detection script but the basic trigger system is not working. Not even the debug messages in the script show up in the console. I've tried with a box collider trigger and a sphere collider trigger (making sure "Is Trigger" is checked of course). The entering objects always have a rigidbody component. So what is the obscure "X-factor" not covered in documentation and tutorials that's got me stymied?

 using UnityEngine;
 using System.Collections;
 
 public class TriggerScript : MonoBehaviour {
 
     void onTriggerEnter(Collider other)
     {
         Debug.Log("Object entered trigger");
     }
 
     void onTriggerExit(Collider other)
     {
         Debug.Log("Object exited trigger");
     }
 
 }