public with sharing class DailyDataSourceContactController {
    public ApexPages.StandardController standardController;
    
     public String recordId{get;set;}
        
    public DailyDataSourceContactController(ApexPages.StandardController standardController)
    {
        this.standardController = standardController;        
         buildPage();
    }
    
    private void buildPage(){
      
      recordId = System.currentPagereference().getParameters().get('id');
      ApexPages.addMessage(new ApexPages.message(ApexPages.severity.ERROR, 'This record is read only. The source system of this record is not salesforce.'));
    } 
}

And my visual force page  is

<apex:page standardController="Contact" extensions="DailyDataSourceContactController" >
            
  <apex:outputPanel >
  <div class="row">
      <div class="span12">
          <div class="alert alert-error failureMsg">             
              <strong><apex:pagemessages /></strong>
           </div>
       </div>
   </div>
</apex:outputPanel>


   <apex:detail subject="{!recordId}" relatedList="true" title="true"/> 


</apex:page>

public with sharing class DailyDataSourceContactController {
    public ApexPages.StandardController standardController;
    
     public String recordId{get;set;}
        
    public DailyDataSourceContactController(ApexPages.StandardController standardController)
    {
        this.standardController = standardController;        
         buildPage();
    }
    
    private void buildPage(){
      
      recordId = System.currentPagereference().getParameters().get('id');
      ApexPages.addMessage(new ApexPages.message(ApexPages.severity.ERROR, 'This record is read only. The source system of this record is not salesforce.'));
    } 
}

And my visual force page  is

<apex:page standardController="Contact" extensions="DailyDataSourceContactController" >
            
  <apex:outputPanel >
  <div class="row">
      <div class="span12">
          <div class="alert alert-error failureMsg">             
              <strong><apex:pagemessages /></strong>
           </div>
       </div>
   </div>
</apex:outputPanel>


   <apex:detail subject="{!recordId}" relatedList="true" title="true"/> 


</apex:page>