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" ng-submit="save(myForm)" novalidate>
        <input type="text" name="txtServiceName" ng-model="ServiceName" required>
<span ng-show="myForm.txtServiceName.$error.required">Enter Service Name</span>
<br/>
          <select name="service_id" class="Sitedropdown" style="width: 220px;"          
                  ng-model="ServiceID" 
                  ng-options="service.ServiceID as service.ServiceName for service in services"
                  required> 
            <option value="">Select Service</option> 
          </select> 
          <span ng-show="myForm.service_id.$error.required">Select service</span>
          
        </form>
    
    Controller:
    
        function Ctrl($scope) {
          $scope.services = [
            {ServiceID: 1, ServiceName: 'Service1'},
            {ServiceID: 2, ServiceName: 'Service2'},
            {ServiceID: 3, ServiceName: 'Service3'}
          ];
    
    $scope.save = function(myForm) {
    console.log('Selected Value: '+ myForm.service_id.$modelValue);
    alert('Data Saved! without validate');
    };
        }
    

Here's a working plunker.