Angular2 subscribing to changes to @Input in Child Component

https://angular.io/docs/ts/latest/api/core/index/Input-var.html

To quote:

Angular automatically updates data-bound properties during change
detection.

If you need to do some processing on the input, look at the get and set.
https://angular.io/docs/ts/latest/cookbook/component-communication.html#!#parent-to-child-setter

From the documentation, here is an example.

import { Component, Input } from '@angular/core';
@Component({
  selector: 'name-child',
  template: `
    <h3>"{{name}}"</h3>
  `
})
export class NameChildComponent {
  _name: string = '<no name set>';
  @Input()
  set name(name: string) {
    this._name = (name && name.trim()) || '<no name set>';
  }
  get name() { return this._name; }
}

You don’t need to use an observable.