Session timeout through Tabs in Browser

Hi,

I have written code for session timeout using javascript. But, there is a small issue which arrised. Issue is, If i have opened a site and opened a link from that site in other tab and i started working on latestly opened tab. So, in the latestly opened tab session time out is working fine. But, in the first tab the session timeout is not getting updated. Because of this alert is shown in first tab. Alert should not be shown as we are working on the same site but in other other tab. Please help me.

Thanks in advance....