.NET component that simplifies tracking of system's idle time

Imports System.ComponentModel
Imports System.Timers
Imports System.Threading
Imports System.Runtime.InteropServices

Public Class SystemIdleTimer
    Inherits Component

    Private Const INTERNAL_TIMER_INTERVAL As Double = 500


    <Description("Event that if fired when idle state is entered.")> _
    Public Event OnEnterIdleState(ByVal sender As Object, ByVal e As IdleEventArgs)
    <Description("Event that is fired when leaving idle state.")> _
    Public Event OnExitIdleState(ByVal sender As Object, ByVal e As IdleEventArgs)

    Private ticker As Timers.Timer
    Private m_MaxIdleTime As Integer
    Private m_LockObject As Object
    Private m_IsIdle As Boolean = False


    <Description("Maximum idle time in miliseconds.")> _
    Public Property MaxIdleTime() As Integer
        Get
            Return m_MaxIdleTime
        End Get
        Set(ByVal value As Integer)
            m_MaxIdleTime = value
        End Set
    End Property
    Public Sub New()
        m_LockObject = New Object()
        ticker = New Timers.Timer(INTERNAL_TIMER_INTERVAL)
        AddHandler ticker.Elapsed, AddressOf InternalTickerElapsed
    End Sub
    Public Sub Start()
        ticker.Start()
    End Sub
    Public Sub [Stop]()
        ticker.Stop()
        SyncLock m_LockObject
            m_IsIdle = False
        End SyncLock
    End Sub
    Public ReadOnly Property IsRunning() As Boolean
        Get
            Return ticker.Enabled
        End Get
    End Property
    Private Sub InternalTickerElapsed(ByVal sender As Object, ByVal e As Timers.ElapsedEventArgs)
        Dim idleTime As UInteger = Win32Wrapper.GetIdle()
        If idleTime > MaxIdleTime Then
            If m_IsIdle = False Then
                SyncLock m_LockObject
                    m_IsIdle = True
                End SyncLock
                Dim args As New IdleEventArgs(e.SignalTime)
                RaiseEvent OnEnterIdleState(Me, args)
            End If
        Else
            If m_IsIdle Then
                SyncLock m_LockObject
                    m_IsIdle = False
                End SyncLock
                Dim args As New IdleEventArgs(e.SignalTime)
                RaiseEvent OnExitIdleState(Me, args)
            End If
        End If
    End Sub
End Class
Public Class IdleEventArgs
    Inherits EventArgs

    Private m_EventTime As DateTime
    Public ReadOnly Property EventTime() As DateTime
        Get
            Return m_EventTime
        End Get
    End Property
    Public Sub New(ByVal timeOfEvent As DateTime)
        m_EventTime = timeOfEvent
    End Sub
End Class
Public Class Win32Wrapper
    Public Structure LASTINPUTINFO
        Public cbSize As UInteger
        Public dwTime As UInteger
    End Structure

    <DllImport("User32.dll")> _
    Private Shared Function GetLastInputInfo(ByRef plii As LASTINPUTINFO) As Boolean
    End Function

    Public Shared Function GetIdle() As UInteger
        Dim lii As New LASTINPUTINFO()
        lii.cbSize = CUInt(Marshal.SizeOf(lii))
        GetLastInputInfo(lii)
        Return (CUInt(Environment.TickCount) - lii.dwTime)
    End Function
End Class