Translation:Shulchan Aruch/Orach Chaim/256
256ː Six Blasts that they used to Blow on the Eve of Shabbat.
1 When the Israelites were settled in their land, they used to blow six blasts on the Eve of Shabbat, to alert the people to separate from the work.
Glossː And the custom in the holy communities is that a half hour or an hour close to Shabbos, an emissary of the community announces to prepare themselves for Shabbat, and this is in place of the blasts that took place in their days. And it is appropriate to act thus in every place.