Zak made the point of:
Is it possible to get an alarm which sounds if the catch of my briefcase
is opened while I am out of the room during a meeting?

I use a soft briefcase like this one:
http://www.crouchandfitzgerald.com/i...cts/hs756p.jpg

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My thoughts so far:

When I have to leave my case unattended maybe I could loop a thin
enamelled wire over some part of the catch so that the wire would get
snapped when the catch was undone. It's not a great way and I'm looking
for something better.

Could some sort of window-catch burglar alarm (with a contact and a
magnet or whatever) be used?

Inside the case I would need a portable but loud alarm sounder which
would respond to a broken circuit. Are there any off-the-shelf products
which would do this?

One of these personal attack alarms designed for people to carry in
their pockets would do this. i use one on my shed. When I open the shed
door, I have to open it only a foot or so and unhook the pin otherwise
when the door is opened fully, the pin comes out and the alarm is
triggered. You can pick them up for a few quid, There was even a site
offering them free a few weeks back.