Shemira before wedding:
The Chasan and Kallah are not to go out alone for several days prior to the wedding. [Practically, many are accustomed to follow this practice one week before the wedding. Others begin to follow it the Shabbos before the wedding, and others from when they arrive in the city the wedding is taking place.]
May two Chasanim and two Kallahs go out together?
May the Chasan or Kallah be home alone?
One time, as the Rebbe was passing by a bank, he saw a Bochur within a week of his wedding standing there without a Shomer. The Rebbe asked him “Where is your Shomer”? The Rebbe then proceeded to stand next to the Bochur acting as his shomer until another Bochur passed by. The Rebbe asked the passing Bochur if he could switch the Rebbe in the Shemirah as he is kind of busy.
 Likkutei Sichos 1:52 that so is a directive from the Rebbe Rayatz; brought in Eternal Joy 2 p.139
 The Rebbe Rayatz did not state an exact amount of days that Shemira is required before the wedding. The previous Rebbe simply stated “several” days. [Likkutei Sichos ibid] Practically, many are accustomed to follow this practice one week before the wedding. Others follow it the Shabbos before the wedding and others from when they arrive in the city the wedding is taking place.
 The reason: The reason for this is because the time before the wedding Mazikim try to interfere with the couple. Having a guard prevents Mazikim from harming the Chasan or Kallah. This is not like the Shemira required after the wedding which is due to respect of the Chasan. [See Likkutei Sichos ibid] However see Elya Raba 669 and Bikurei Yaakov 669:3 that a Chasan is considered a king for a week before the wedding.
 Rav Shmuel Levitin as he received from the Rebbe, recorded in Kovetz Chasuna p. 41
 The reason: As the reason behind this Shemira is due to Mazikin and not due to being similar to a king
 Aruch Hashulchan 64:3 regarding after the wedding due to the reason of Mazikin, and the same should apply before the wedding
 Diary of Rav Groner “The Rebbe Rayatz told the Rebbe not to be alone in a room without a Shomer, and not to pass from room to room without a Shomer”.
 Heard from Rav Yehuda Leib Groner