before_filter :session_expire

private

def session_expire
  if session[:user]
    session_length = 60*10 #10 Minutes for logged in users
    expire_time = session[:expire_time] || Time.now + 10
    if expire_time < Time.now
      reset_session
      flash[:notice] = "You have been logged out due to an extended period of inactivity"
      redirect_to :controller => 'welcome' , :action => 'index'
    else
      session[:expire_time] = Time.now + session_length
    end
  end
end

before_filter :session_expire

private

def session_expire
if session[:user]
session_length = 60*10 #10 Minutes for logged in users
expire_time = session[:expire_time] || Time.now + 10
if expire_time < Time.now
reset_session
flash[:notice] = "You have been logged out due to an extended period of inactivity"
redirect_to :controller => 'welcome' , :action => 'index'
else
session[:expire_time] = Time.now + session_length
end
end
end

ruby session expire

Ruby