Daemons can have any ppid and a ppid of 1 is no guarantee that you're a daemon. I like the open /dev/tty idea. It's portable. But of course it can fail for other reasons. No one ever did a
rm /dev/tty
on any of your systems? Also the process could be out of fd's, etc. Still it's the best way. Depending on the unix system, ther may be a non-portable way. Get the source code for ps and see how it finds this stuff out. But that is a lot of trouble to avoid opening /dev/tty. I would go with that.