debounce angular 2 with ngModelChange

I have a ngModelChange on a textArea like this :

      <ion-textarea placeholder="Type your message here" formControlName="message" [(ngModel)]="message" (ngModelChange)="changing($event)"></ion-textarea>

And now I'd like to know where the user is typing on this textarea or not, so I'd like to use debounce with a timmer of 5000 for example to know if he's typing or not, not sending for every letter he's typing, I want to fire this event every 5 seconds, how could I implement it?