Siman 256
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א כְּשֶׁהָיוּ יִשְׂרָאֵל בְּיִשּׁוּבָן, הָיוּ תּוֹקְעִין בְּעֶרֶב שַׁבָּת שִׁשָּׁה תְּקִיעוֹת, כְּדֵי לְהַבְדִּיל אֶת הָעָם מִן הַמְּלָאכָה. הַגָּה: וְנָהֲגוּ בַּקְּהִלּוֹת הַקְּדוֹשׁוֹת, שֶׁכָּל שֶׁהוּא סָמוּךְ לְשַׁבָּת כְּחֵצִי אוֹ שָׁעָה, שֶׁמַּכְרִיז שְׁלִיחַ צִבּוּר לְהָכִין עַצְמָן לְשַׁבָּת, וְהוּא בִּמְקוֹם הַתְּקִיעוֹת בִּימֵיהֶם, וְכֵן רָאוּי לִנְהֹג בְּכָל מָקוֹם.
1 The Six Shofar Blasts that Would Be Sounded on Friday: When the Jewish people were settled in their land, they used to sound six shofar blasts on Erev Shabbat, [to alert] the people to conclude [their] work. Rema: At present, the custom in holy communities is that a half hour or an hour before Shabbos, an emissary of the community announces [that everyone] should prepare himself for Shabbat, and this is in place of the shofar blasts that took place in those days. It is appropriate to act thus in all places.