Question OnTriggerStay sometimes doesn't trigger?

It triggers sometimes when you stay still inside the collider but other times you have to move in order to trigger it. Sometimes I have to press the e key five times to get it to trigger. The collider is quite big so that's not it, I thought maybe it was my script?

Code (CSharp):

1.  
2. void OnTriggerStay(Collider other) {
3.  
4.         if (Input.GetKeyDown("e"))
5.         {
6.             if (other.CompareTag("Player"))
7.             {
8.                 if(ButtonAnimator.GetBool("Down") == false) {
9.                     ButtonAnimator.SetBool("Down", true);
10.                     // This is here to try to get the animation to play before the sound
11.                     SawAnimator.SetTrigger("SawAnimationTrigger");
12.                     audio.clip = idle;
13.                     audio.loop = true;
14.                     audio.PlayDelayed(13);
15.                 } else {
16.                     ButtonAnimator.SetBool("Down", false);
17.                     SawAnimator.SetTrigger("SawAnimationTrigger");
18.                     audio.Stop();
19.                 }
20.             }
21.         }
22.  
23.     }
24.  

 

This is Physics problem: OnTriggerStay may not be called on every (visual) frame, so it has a chance to be not called when GetKeyDown("e") is true.
Physics event functions will be called only when Physics decide to evaluate this frame (= when FixedUpdate is called).