AngularFireAuthGuard

auth.guard.ts

import { Injectable } from '@angular/core';
import { CanActivate, ActivatedRouteSnapshot, RouterStateSnapshot, Router } from '@angular/router';
import { Observable } from 'rxjs/Observable';
import { AngularFire } from 'angularfire2';

import 'rxjs/add/operator/map';

@Injectable()
export class AuthGuard implements CanActivate {
  constructor(private af: AngularFire, private router:Router) {}

  canActivate(
    next: ActivatedRouteSnapshot,
    state: RouterStateSnapshot): Observable<boolean> {
    return this.af.auth.map(auth => {
      if (auth !== null){
        return true;
      }
      this.router.navigate(['/login'])
    });
  };
}

It can even be (a bit) simpler:

import { Injectable } from '@angular/core';
import { CanActivate, Router } from '@angular/router';
import { Observable } from 'rxjs/Observable';
import { AngularFire } from 'angularfire2';

import 'rxjs/add/operator/map';

@Injectable()
export class AuthGuard implements CanActivate {
  constructor(private af: AngularFire, private router:Router) {}

  canActivate(): Observable<boolean> {
    return this.af.auth.map(auth => {
      if (auth !== null){
        return true;
      }
      this.router.navigate(['/login'])
    });
  };
}