What might be grabbing devices?

[Ross Boylan <RossBoylan@stanfordalumni.org>]

I know that the desktop monitors for new devices because when I insert
a dvd a window pops up asking me what I want to do.  For cd/dvd
burning I'm advised to turn off other things that access the device
(though I also gather the problems k3b is having verifying probably
lie elsewhere).

More immediately, I'm having trouble faxing and one possibility is
that something is interefering with /dev/ttyS0.

Does anyone know what exactly might be doing such things, and how I
can disable it?  I've seen some suggestion that hal is the culprit,
but nothing definite.

The system with the fax trouble is Debian testing, KDE 3.5, 2.4 kernel
(i.e, not udev).  The one with the dvd is running 2.6.15 kernel with
udev.

Thanks.
Ross Boylan