"והיה מחניך קדוש" - Keeping the Jewish Camp Holy (95)
Preserving our Kedusha: Yichud. In order to distance a Jew from temptation to sin, the Torah prohibits a man and a woman who is forbidden to him - either because she is married, or she is a relative, e.g. a mother-in-law - from being alone together in a secluded place. This is defined as a closed room or a place where other people will probably not come to and they will remain alone. The Sages extended this to include other women and unmarried girls, both Jewish and gentile. They even prohibited some cases where more than one man and/or woman are there, as will be explained IY”H. This issur not only prohibits one from entering the secluded area, it also obligates him to leave the area if he realizes that he is alone with a lady.
When in Doubt. If a person has a doubt about Yichud (e.g. he is not sure if a woman is in the house alone with him or he is not sure if the girl in the house is younger than three years old) - in cases where it is a Torah prohibition, one certainly must be strict since "ספיקא דאורייתא לחומרא". Even where it is at most a Rabbinic issur (מדרבנן), R’ Shmuel Wosner zt”l held that one should be strict for a number of reasons that he mentions (1).
While Doing a Mitzvah. Sometimes a person will be in the act of doing a mitzvah and the question of Yichud comes up. For example, while performing mitzvos like Bikur Cholim, Hachnasas Orchim, visiting a doctor to take care of one’s health, etc., one must be careful to ensure that the place where he is is not considered “secluded.” However, for the mitzvah of saving a life, we rely on contemporary Poskim (2) who are lenient in this issue. If a woman or a girl require transport to deliver a baby, or for a serious medical condition, it is permitted for a man to drive her, even through quiet side streets (secluded), at late hours (no people are around), even in a car with tinted windows. Similarly, if a Hatzala worker arrives at an apartment where the door will lock once he is inside and he will be alone with a lady as he tries to save her life, it is permitted. This is true even if he knows that no other Hatzala members are able to come, because if others are on their way, it is then deemed a "פתח פתוח לרשות הרבים" - an area that is open to a public place, which is not a problem as far as Yichud.
Older People. The issur of Yichud applies to people of all ages, no matter how old and infirm the parties might be. This has a common application. If an old man lives alone and he is entitled (by the government or insurance) to have a female aide assist him, there is still a question of Yichud. A possible solution might be to give a house or apartment key to a number of neighbors who will at random enter the elderly man’s home at any time of night or day. Of course, this should be done under direction of a Rav, due to many potential complications.
(1) שו"ת שבט הלוי ג:קפג, ה:רה (2) עיין שו"ת שבט הלוי ו:לח ושו"ת ציץ אליעזר ו:מ:יב