I determine whether I'm remote using this C program I wrote.  I've
tested it only linux.  It uses the fact that most well-behaved remote
login daemons make sure that your tty's utmp entry contains the host
from which you logged in if you are logged in remotely.  This program
prints "local" if you're local, "remote" if you remote, and a few
other things if it can't tell for various reasons.  I've found it to
accurately detect remote logins with ssh, telnet, and (Kerberos)
rlogin and to accurately detect local logins with or without X.  If
you remote login back to your local host (for some reason) it still
considers you to be local.