13th of Tebet, 5770
The custom today is to put a Mezuzah on virtually every door of the house. Therefore, a Jewish home has Mezuzot on the front and side doors, porch, bedrooms, living room, kitchen, playroom, etc. The exceptions are: Bathrooms and rooms with an area smaller than 36 square feet. If a room has more than one door, one Mezuzah is required for every door.
On an entrance without a door we should put a Mezuzah but without saying a berakha for that specific Mezuzah, because this is a case of a Halakhic controversy (Machloket between HaRambam and the Rosh). Alternatively, when affixing another Mezuzah in the house and saying the berakha for it, have in mind the entrance Mezuzah and affix it afterwards.
In addition to private places of residence, a Mezuzah should also be affixed in businesses, offices and stores, when they belong to a Jewish owner.
Read: “Mezuzah and surveillance” http://www.aish.com/jl/m/48971621.html