Código:
<html> <head> <script> function redireccionar(){ if(screen.width>=800){ location.href="http://www.miweb.cl/movil/movil.php"; }else{ location.href="http://www.miweb.cl/movil/sitio/web_mov.php?anchoscr=" + screen.width; } } </script> </head> <body onLoad="redireccionar()"> </body> </html>