Finding my security system

[rbrooks@xxxxxxxxx]

We bought a new house a few months ago.  It was only  yesterday that I
noticed our sliding door in the back has a sensor on it with an ADT
logo.  It has a wire from it that goes up in the wall, but that's the
only trace i've been able to find.  I know it can't be TOO old, because
the back of the house (where this is) is part of an addition that was
put on.  I've never had anything like this before, so I don't know even
where to look about to find where the control panel once was.  I'm
interested to know though, because I've been considering getting a
system anyway, and this would be great (cheaper) if there's more.
Would I be able to call ADT and could they tell me what once was here?