AngularJS Dropdown required validation

Following is my code snippet. I want to validate my dropdown using angular. 

<td align="left" width="52%"> 
  <span class="requiredSmall">*</span> 
    <select class="Sitedropdown" style="width: 220px;" 
            ng-model="selectedSpecimen().serviceID" 
            ng-options="service.ServiceID as service.ServiceName for service in services"> 
         <option value="" ng-selected="selected">Select Service</option> 
   </select> 
</td>

Valid means:

Valid values can be anything but "Select Service", it is my default value. Like other ASP.net Require field validator DefaultValue="0" for dropdown, so here My dropdown will be bound from the services and I want to select all other values except "Select Service".

You need to add a 'name' attribute to your dropdown list, then you need to add a required attribute, and then you can reference the error using myForm.[input name].$error.required:

HTML:

<form name="myForm" ng-controller="Ctrl">

  <select name="service_id" class="Sitedropdown" style="width: 220px;"          
          ng-model="ServiceID" 
          ng-options="service.ServiceID as service.ServiceName for service in services"
          required> 
    <option value="">Select Service</option> 
  </select> 
  <span ng-show="myForm.service_id.$error.required">Select service</span>

</form>

Controller:

function Ctrl($scope) {
  $scope.services = [
    {ServiceID: 1, ServiceName: 'Service1'},
    {ServiceID: 2, ServiceName: 'Service2'},
    {ServiceID: 3, ServiceName: 'Service3'}
  ];
}

This is the code used in plunker that actually works! 

  <select name="service_id" class="Sitedropdown" style="width: 220px;"          
      ng-model="ServiceID" 
      ng-options="service.ServiceID as service.ServiceName for service in services"
      required> 
  <option value="">Select Service</option> 
 </select> 
 <span class="error" ng-show="myForm.service_id.$dirty && myForm.service_id.$invalid">Select service</span>
 </form>