How to trigger change event of checkbox after model value change? Angular 4

I want to trigger change event of checkbox two on checking on checkbox one. So far after second one is checked when first one is checked. But I couldn't get second one to fire its change event Here's my code This is my template code

<input [ngModel]="firstOne" (ngModelChange)="someEvent($event)" type="checkbox">
<input [ngModel]="secondOne" (ngModelChange)="secondEvent($event)" type="checkbox">

Controller code

this.firstOne:boolean=false;
this.secondOne:boolean=false;

constructor(){}
someEvent(event){
  this.secondOne = true;
}

secondEvent(event){
 alert("second is triggered")
}

Thanks for any suggestion.