7. It is a mitzvah to light the Chanukah candles [outside] in an entrance
that opens to the street ("reshus ha'rabim") in order to publicize the
miracle. This was the practice in the era of the Mishnah and the Gemara (1).
At present, when we live among the Gentiles, one should light the candles
inside one's home (2). If one has a window that overlooks the street, one
should light them there. If not, one should light them in the doorway
[inside the home].
It is a mitzvah to place the candles within a handbreadth ("tefach") (3) of
the entrance on the left side, so that the mezuzah will be on the right,
and Chanukah candles on the left, and thus, one will be surrounded by
mitzvos. Preferably, one should place [the menorah] in the doorway itself
(that is, in line with the two door posts, but towards the left (4)).
(1) It is still the custom in Israel today to light the Chanukah candles
outside in a glass box, next to the entrance that opens to street.
(2) Many say that the custom to light inside developed as a result of the
cold, snowy and windy weather that often occurs during Chanukah time in
Europe and North America. Also, at certain points throughout Jewish
History, it was dangerous to light outside due to anti-semitism, and some
authorities mention that theft was a problem at times.
(3) Opinions among the authorities as to the exact length of a 'tefach'
('handbreadth') range between 8 and 10cm ( 3 to 4 inches).
(4) See Mishna Berura 671:36.