Web Forms :: Store Logout Time In Database When User Closes Tab Or Browser

I want to kill the session on the browser closing or tab closing and store the Logout time in database using Asp.Net.

I have coded that code in Global.asax page which works only when we Click on Logout Button .but it's not worked on the tab closing /Browser closing.

void Session_End(object sender, EventArgs e) {
SqlTransaction transaction = null;
using (SqlConnection con = new SqlConnection(conn)) {
con.Open();
SqlCommand cmd = con.CreateCommand();
transaction = con.BeginTransaction("Transactions");

[Code] ....