Asp.net Detecting Session timeout and redirection

If you are using Basepage logic its better to use this code there.

Redirection logic is written for pages with Frames or without Frames

Protected Overrides Sub OnPreRender(ByVal e As System.EventArgs) MyBase.OnPreRender(e)
If context.Session.IsNewSession = True Then
Dim strCookieHeader As String = Page.Request.Headers("Cookie")
If Not strCookieHeader Is Nothing Then
strCookieHeader = strCookieHeader.ToLower
End If

'Checking for duplicate Session.
If Not strCookieHeader Is Nothing AndAlso strCookieHeader.IndexOf("asp.net_sessionid") >= 0 Then
If Page.Request.IsAuthenticated = True Then
System.Web.Security.FormsAuthentication.SignOut()
End If

'If you want to redirect to defaultpage you can use this
'Page.Response.Redirect("default.aspx?Timeout")

'If you are using Frames then this will work.
Response.Write("window.open('default.aspx?Timeout','_parent');")
End If
End If
End Sub