does header("Location: n") work on non-browser agents?

My site uses a scheme whereby a session variable (say, $logged_in) is checked for. If the variable is not set to 1, then header("Location: ./index.php") is used to redirect the browser to index.php, where they are offered an opportunity to log in (setting the session variable $logged_in to 1). But then I thought to myself, could this page still be accessed by a script or a spider, or some other agent besides a browser? I don't know much about how HTTP works, but I am wondering if this is an adequate means of protecting my site from unlogged-in visitors. TIA, Erik ---- Erik Price Web Developer Temp Media Lab, H.H. Brown pricee@hhbrown.com