Venice has a low crime rate, but many people take home security seriously. For example, the key will turn several times in the door lock, with each turn putting into place another set of bolts.
Another area where you will see methods of home security displayed is at the tops of fences that could be reached by someone with determination (and a ladder, in some cases). I guess it also deters pigeons, cats and anything else that climbs or perches.
So, here is how to use those empty wine and beer bottles.