Laptop power disconnect alarm

[Bram Neijt <bneijt gmail com>]

Dear GNOME developers,

I have  a program idea that I would like to create and test out, but I
have no idea whether something like this has already been created and
what documentation to read in order to create it.

I want an application that will sound an alarm if my laptop adapter is
unplugged while the screen is locked. The idea is that if somebody tries
to steal my locked laptop, disconnecting the power, it will start
shouting "I'm being stolen!" (by playing a sound file).

Because it needs both power information and screen-lock information and
is laptop specific, I think a separate program is needed. The questions
I have are:

- How do I keep an eye on the power status? What interface should I
register, dbus something??
- How do I keep an eye on the screen-saver status, where can I register
for locking/unlocking events?
- Is there something like this already created, would it be scriptable
instead of programming it out completely?

For most of these questions, links would suffice. Any ideas are of
course also welcome.

Greetings,
  Bram Neijt