Shows how to detect any touch of the iOS screen

CustomApp.cs

public class Application
    {
        // This is the main entry point of the application.
		static void Main(string[] args)
		{
			UIApplication.Main(args, typeof(CustomApplication), typeof(AppDelegate));
		}
    }

	// Inherits from UIApplication
	public class CustomApplication : UIApplication
	{
	  // This gets called for various system events.
		public override void SendEvent (UIEvent ev)
		{
			base.SendEvent (ev);
			
			//Check if the screen was touched. This will always be called, no matter what view controller is currently on screen.
			UITouch anyTouch = ev.AllTouches != null ? ev.AllTouches.AnyObject as UITouch : null;
			if(anyTouch != null && anyTouch.TapCount > 0 && anyTouch.Phase == UITouchPhase.Began)
			{
				// TODO: Update some static variable or database value to store the current time of the touch
			}
		}
	}