You can do by workflow rule or Trigger

I am sending one sample trigger.You can write trriger for Contact object 

trigger Email_Notification on Technician_Assignment__c (after insert,after update) 
  {
    LIST<Technician_Assignment__c > ta= trigger.new;

   Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
        if(tech.Employees__r.E_mail__c!=null)
          {
            String[] etoaddress=new String[]{tech.Employees__r.E_mail__c};
            mail.setToAddresses(etoaddress);
          }
        if(tech.Contact__r.email!=null)
          {
            String[] ctoaddress=new String[]{tech.Contact__r.email};  
            mail.setToAddresses(ctoaddress);
          }
        mail.setsubject('Service Order Activity Information');
        mail.setPlainTextBody('Service Order ID: '+activity.Service_Order__r.Name+'\n\n'+'Activity Step No : ' +activity.Name+ '\n\n'+ 'Priority : '+activity.Priority__c );
        Messaging.sendEmail(new Messaging.SingleEmailMessage[] {mail});
        User u = [SELECT id,name FROM User WHERE Email=:tech.Employees__r.E_mail__c ];
        Task t = new Task(ownerId = u.id,  Subject='Service Order Avtivity', ActivityDate=ta[0].Activity__r.Date__c, whatid=ta[0].id  );   
        insert t;
      }

If your question is resolved please mark it as accept as a solution, If not please let me know.