Observe services from controllers

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

controllers.my-route-1.js

import Ember from 'ember';

export default Ember.Controller.extend({
  'my-service': Ember.inject.service('my-service'),
  prop: Ember.computed('my-service.prop', function(){
    return this.get('my-service.prop');
  }),
  actions: {
    changeServiceValue(){
     this.get('my-service').set('prop', Ember.Object.create({value: Math.random()})); 
    }
  }
});

controllers.my-route-2.js

import Ember from 'ember';

export default Ember.Controller.extend({
  someService: Ember.inject.service('my-service'),
  queryParams: ['someValue'],
  someValue: Ember.computed('someService.prop.value', function(){
    console.log('prop changed in controller 2');
    return this.get('someService.prop.value');
  })
});

router.js

import Ember from 'ember';
import config from './config/environment';

const Router = Ember.Router.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
      this.route('my-route-1');
      this.route('my-route-2');
});

export default Router;

routes.my-route-1.js

import Ember from 'ember';

export default Ember.Route.extend({
  
});

routes.my-route-2.js

import Ember from 'ember';

export default Ember.Route.extend({
  queryParams: {
    someValue:{
      refreshModel: true
    }
  },
  model(){
    return new Ember.Object({});
  }
});

services.my-service.js

import Ember from 'ember';

export default Ember.Service.extend({
  prop: null
});

templates.application.hbs

{{#link-to 'my-route-1'}}Go To Route 1{{/link-to}}
{{#link-to 'my-route-2'}}Go To Route 2{{/link-to}}
<br>
<br>

{{outlet}}

templates.my-route-1.hbs

<h1>Route 1</h1>

<p>Value is : {{prop.value}}</p>
<button {{action 'changeServiceValue'}}>Change my value</button>

templates.my-route-2.hbs

<h1>Route 2</h1>
<p>Value is: {{someValue}}</p>

twiddle.json

{
  "version": "0.10.4",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.7.0",
    "ember-data": "2.7.0",
    "ember-template-compiler": "2.7.0"
  },
  "addons": {}
}