using the ng change in angular 2 using ng model variable

You could use the ngModelChange event:

[(ngModel)]="variable" (ngModelChange)="doSomething($event)"

Edit

According to your comment, I think that you should use form control with a custom validator.

Here is a sample:

@Component({
  (...)
  template: `
    <input [(ngModel)]="variable" [ngFormControl]="ctrl"/>
  `
})
export class SomeComponent {
  constructor() {
    this.ctrl = new Control('', (control) => {
      // validate the value
    });

    this.ctrl.valueChanges.subscribe((value) => {
      // called when the value is updated
    });

  }
}

See this article for more details:

• http://restlet.com/blog/2016/02/11/implementing-angular2-forms-beyond-basics-part-1/