What do luxury residences and prisons have in common?

A friend pointed out to me the many security cameras on the fence of a luxurious (at least in price) private residence along the waterfront next to the Science Park.  

I observed similar set ups at another private residence along Clear Water Bay Road.  In fact, fences, barbed wires, security cameras surround a lot of such private spaces. 

The curious thing is that the same set up can be seen at the Pik Uk Prison along Clear Water Bay Road. 

And other such facilities, such as Siu Nam psychiatric hospital.

There is one crucial difference, of course.  At the prisons, the barbed wires and security cameras face inside, to prevent the inmates from escaping.  At the luxury private residences, on the other hand, the security cameras watch the outside, to prevent people from getting in.  

It is a sign that the rich and powerful, from which the ruling class is drawn, live apart from the rest of us.  They are afraid of mingling with the rest of us.