equivalence of $ .watch of angularJS 1.x in angular 6

I have a sidebar and an Angular Material toolbar that should only be shown if the user is logged in.

Now, I have a service to determine if the user is logged in that has a method that returns true / false.

The problem is that the login is a different component to the sidebar and the toolbar; so when you login, the initial true / false value of these components is not updated.

in angularJS could add a $ .watch (); Is there something similar in angular6? or another way to update the value of a variable of a component from another component?

my service:

import { Injectable } from '@angular/core';
import { Router } from '@angular/router';
import { Http, Response } from '@angular/http';
import { map } from 'rxjs/operators';

@Injectable({
  providedIn: 'root'
})
export class SessionService {

  constructor(private router:Router, private http:Http) { }

  IslogIn(){
    if(sessionStorage.getItem("Id")!==null){
      return true;
    }else{
      return false;
    }
  }
}

my app.component.ts:

import { Component } from '@angular/core';
import {NotificacionesService} from "./services/notificaciones.service";
import {SessionService} from "./services/sesion.service";

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'Aces SRL ';
  estado= false;
  logueado:boolean = false;

  constructor(private Notif:NotificacionesService, private Sesion:SessionService){
      this.MisNotif = this.Notif.FnNotificaciones(1);
      this.cant = this.MisNotif.length;
      this.logueado = this.Sesion.IslogIn();
    }
}

My app.component.html (fragment)

<mat-drawer-container>
    <mat-drawer #drawer class="example-sidenav" mode="side" opened="true" [hidden]="!logeado">
      <app-menu></app-menu>
    </mat-drawer>

    <!--  Contenido-->
    <div class="example-sidenav-content">

    </div>
      <router-outlet></router-outlet>
    <button type="button" mat-button="mat-button" (click)="drawer.toggle()">Toggle sidenav</button>
  </mat-drawer-container>

Your support is appreciated in advance.

salu2!