Thank You guys!
Yup.. you could drill a sample hole in wall in order to see what is beyond, but there are some places where drilling is simply not possible or it may take a lot of drilling in order to find the best place to put fixtures or support pillars for staircases. Also, it would be nice to somehow screen the range of available places for putting the pillars and to see where it would be more convenient.
You are also right about the ages and possible bulding material. We are facing now with different story here. A majority of houses are private built, with no available documentation (plans and cross sections) and of course, there are always construction worker who are not always building according to blueprints.
Anyway... this remains as really interesting question as it is not only problem for me, but a whole lot of repairman and friends who work on installation jobs face the similar problems.
Something like finding the wires in the wall... but more delicate