This class detects USB devices attached/removed to the system.

using System;
using System.Management;

namespace X_ToolZ.Helpers
{
	class DriveDetector
	{
		static ManagementEventWatcher managementEventWatcher;
		public delegate void USBDeviceAddedEventHandler(string driveLetter);
		public event USBDeviceAddedEventHandler USBDeviceAdded;

		public delegate void USBDeviceRemovedEventHandler(string driveLetter);
		public event USBDeviceRemovedEventHandler USBDeviceRemoved;

		public DriveDetector()
		{
			WqlEventQuery wqlEventQuery = new WqlEventQuery();
			wqlEventQuery.EventClassName = "__InstanceOperationEvent";
			wqlEventQuery.WithinInterval = new TimeSpan(0, 0, 3);
			wqlEventQuery.Condition = @"TargetInstance ISA 'Win32_DiskDrive'";

			ManagementScope managementScope = new ManagementScope("root\CIMV2");
			managementScope.Options.EnablePrivileges = true;
			managementEventWatcher = new ManagementEventWatcher(managementScope, wqlEventQuery);
			managementEventWatcher.EventArrived += new EventArrivedEventHandler(managementEventWatcher_EventArrived);
			managementEventWatcher.Start();
		}

		public void Start()
		{
			managementEventWatcher.Start();
		}

		public void Stop()
		{
			managementEventWatcher.Stop();
		}

		void managementEventWatcher_EventArrived(object sender, EventArrivedEventArgs e)
		{
			bool isUSBEvent = false;
			string deviceName = string.Empty;

			foreach (PropertyData propertyData in e.NewEvent.Properties)
			{
				ManagementBaseObject managementBaseObject = (ManagementBaseObject)propertyData.Value;
				if (managementBaseObject != null)
				{
					foreach (PropertyData propertyDataSub in managementBaseObject.Properties)
					{
						if (propertyDataSub.Name == "Caption")
						deviceName = propertyDataSub.Value.ToString();
						if (propertyDataSub.Name == "InterfaceType" && propertyDataSub.Value.ToString() == "USB")
						{
							isUSBEvent = true;
							break;
						}
					}

					if (isUSBEvent)
					{
						if (e.NewEvent.ClassPath.ClassName == "__InstanceCreationEvent")
						{
							if (USBDeviceAdded != null)
							USBDeviceAdded(deviceName);
						}
						else if (e.NewEvent.ClassPath.ClassName == "__InstanceDeletionEvent")
						{
							if (USBDeviceRemoved != null)
							USBDeviceRemoved(deviceName);
						}
					}
				}
			}
		}
	}
}

Usage:

private static readonly DriveDetector driveDetector = new DriveDetector();

private void StartDetection()
{
	driveDetector.USBDeviceAdded += new DriveDetector.USBDeviceAddedEventHandler(driveDetector_USBDeviceAdded);
	driveDetector.USBDeviceRemoved += new DriveDetector.USBDeviceRemovedEventHandler(driveDetector_USBDeviceRemoved);
	driveDetector.Start();
}

private void StopDetection()
{
	driveDetector.Stop();
}

private void driveDetector_USBDeviceAdded(string driveLetter)
{
	//Custom logic here
}

private void driveDetector_USBDeviceRemoved(string driveLetter)
{
	//Custom logic here
}