UsbDetector

#nullable enable
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Management;
using System.Reactive.Linq;
using System.Reactive.Subjects;

    /// <summary>
    /// <a href="https://stackoverflow.com/questions/620144/detecting-usb-drive-insertion-and-removal-using-windows-service-and-c-sharp"/>
    /// </summary>
    public class UsbDetector 
    {
        private const string Query = "SELECT * FROM {0} WITHIN 2 WHERE TargetInstance ISA 'Win32_USBHub'";
        private const string CreationEvent = "__InstanceCreationEvent";
        private const string DeletionEvent = "__InstanceDeletionEvent";
        private const int ReplayNumber = 1;

        private readonly Subject<USBDeviceInfo> adds = new Subject<USBDeviceInfo>();
        private readonly Subject<USBDeviceInfo> removes = new Subject<USBDeviceInfo>();

        public UsbDetector()
        {
            var bgwDriveDetector = new BackgroundWorker();
            bgwDriveDetector.DoWork += DoWork;
            bgwDriveDetector.RunWorkerAsync();
        }

        public IObservable<USBDeviceInfo> Adds => adds.AsObservable();

        public IObservable<USBDeviceInfo> Removes => removes.AsObservable();


        private void DoWork(object sender, DoWorkEventArgs e)
        {
            SubscribeToEvent(CreationEvent, adds);
            SubscribeToEvent(DeletionEvent, removes);
        }

        private static void SubscribeToEvent(string eventType, IObserver<USBDeviceInfo> observer)
        {
            WqlEventQuery wqlEventQuery = new WqlEventQuery(string.Format(Query, eventType));
            ManagementEventWatcher insertWatcher = new ManagementEventWatcher(wqlEventQuery);
    
            var observable = Observable.FromEventPattern<EventArrivedEventHandler, EventArrivedEventArgs>(
                h => insertWatcher.EventArrived += h,
                h => insertWatcher.EventArrived -= h).Replay(ReplayNumber);

            observable.Connect();
            observable.Select(a => a.EventArgs).Select(MapEventArgs).Subscribe(observer);
            insertWatcher.Start();
        }


        private static USBDeviceInfo MapEventArgs(EventArrivedEventArgs e)
        {
            ManagementBaseObject instance = (ManagementBaseObject)e.NewEvent["TargetInstance"];

            //string appDataPath = System.Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
            string deviceId = (string)instance.GetPropertyValue("DeviceID");
            string serialNr = deviceId.Substring(deviceId.LastIndexOf('\\')).Replace("\\", "");
            char? driveLetter = GetDriveLetter(serialNr)?.First();

            return new USBDeviceInfo(deviceId, serialNr, driveLetter);
        }



        public struct USBDeviceInfo
        {

            public USBDeviceInfo(string deviceId, string SerialNr, char? driveLetter)
            {
                this.DeviceId = deviceId;
                this.SerialNr = SerialNr;
                DriveLetter = driveLetter;
            }

            public string DeviceId { get; }

            public string SerialNr { get; }

            public char? DriveLetter { get; }

            public override string ToString() => $"DeviceId: {DeviceId}; SerialNr: {SerialNr}; DriveLetter: {DriveLetter}";
        }

        /// <summary>
        /// https://stackoverflow.com/questions/31938686/how-to-get-the-drive-letter-of-usb-device-using-wmi
        /// </summary>
        /// <returns></returns>
        static IEnumerable<(string deviceId, string pnpDeviceId, string? driveLetter)> SelectDeviceInformation()
        {
            foreach (ManagementObject device in SelectDevices())
            {
                var deviceId = (string)device.GetPropertyValue("DeviceID");
                var pnpDeviceId = (string)device.GetPropertyValue("PNPDeviceID");
                var driveLetter = (string?)SelectPartitions(device).SelectMany(SelectDisks).Select(disk => disk["Name"]).SingleOrDefault();

                yield return (deviceId, pnpDeviceId, driveLetter);
            }

            static IEnumerable<ManagementObject> SelectDevices() => new ManagementObjectSearcher(
                    @"SELECT * FROM Win32_DiskDrive WHERE InterfaceType LIKE 'USB%'").Get()
                .Cast<ManagementObject>();

            static IEnumerable<ManagementObject> SelectPartitions(ManagementObject device) => new ManagementObjectSearcher(
                    "ASSOCIATORS OF {Win32_DiskDrive.DeviceID=" +
                    "'" + device.Properties["DeviceID"].Value + "'} " +
                    "WHERE AssocClass = Win32_DiskDriveToDiskPartition").Get()
                .Cast<ManagementObject>();

            static IEnumerable<ManagementObject> SelectDisks(ManagementObject partition) => new ManagementObjectSearcher(
                    "ASSOCIATORS OF {Win32_DiskPartition.DeviceID=" +
                    "'" + partition["DeviceID"] + "'" +
                    "} WHERE AssocClass = Win32_LogicalDiskToPartition").Get()
                .Cast<ManagementObject>();
        }


        
        private static string? GetDriveLetter(string serialNr)
        {
            return SelectDeviceInformation()
               .SingleOrDefault(a =>
               a.pnpDeviceId.Remove(a.pnpDeviceId.Length - 2).Substring(a.pnpDeviceId.LastIndexOf('\\')).Replace("\\", "") ==(serialNr)).driveLetter;
        }
    }

@elmazzun Thank you very much

You are welcome!
I am not a C# expert but you should be able to get something working out of my repo.