QuickOPC User's Guide and Reference
Examples - Reactive Programming - Create OPC A&E observable and subscribe
// Shows how to create an observable for OPC-A&E notifications, and subscribe to it.

using System;
using System.Threading;
using OpcLabs.EasyOpc.AlarmsAndEvents.Reactive;

namespace ReactiveDocExamples
{
    namespace _AENotificationObservable
    {
        class Subscribe
        {
            public static void Main1()
            {
                Console.WriteLine("Creating observable...");
                AENotificationObservable events =
                    AENotificationObservable.Create("", "OPCLabs.KitEventServer.2", 1000);

                Console.WriteLine("Subscribing...");
                using (events.Subscribe(e => Console.WriteLine(
                    (e.Exception is null) ? (e.EventData?.Message ?? "") : e.Exception.GetBaseException().ToString())))
                {
                    Console.WriteLine("Waiting for 10 seconds...");
                    Thread.Sleep(10*1000);

                    Console.WriteLine("Unsubscribing...");
                }

                Console.WriteLine("Waiting for 2 seconds...");
                Thread.Sleep(2 * 1000);
            }
        }
    }
}
See Also

Conceptual

Examples - OPC Alarms&Events