Prof installed, unmonitored, wireless system... advice?

[Wug]

We have a second floor condo which has a private first floor
entrance, a sliding glass door which opens onto a balcony, and
ten windows. Drop down stairs lead to an unfinished attic from
which one could fairly easily drop wires down to everything but
the main entrance. The main entrance is a single story section
which sticks out from the building, and I can't imagine any way
of fishing wires to a sensor or control panel without mucking up
the drywall/paint (which I'd like to avoid if at all possible). This
is a safe condo community with plenty of neighbors home at any
given time of day. ATM at least, I'm not terribly interested in a
monitoring service or fire/smoke detection. It would be nice if
those could be easily added down the road, but for now an
appropriately loud siren upon breakin would be adequate I think.

I've started to read up on the subject and this coming week I'll
ping a couple of reputable local companies. But I thought I'd
also ping you folks to see if you have any advice wrt specific
systems or hookup strategies or whatever. Thanks in advance.