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Appointing others to help one perform the Bedika:
Appointing others versus doing oneself: A homeowner may appoint another person in his place to perform the Bedika of his home, and have that person say the blessing. Nevertheless, it is proper for the homeowner to search the [entire] house himself rather than appoint others to do so for him. However, if one is unable to check all the rooms himself, then he should [at least] check one room or one corner, and appoint family members to check the remaining areas. [Furthermore, some learn that it is encouraged to merit others [males above the age of 13] to participate in the Mitzvah of Bedika, rather than have the father of the home perform the entire Bedika himself.]
Do the emissaries say a separate blessing? In a case that the emissaries will be doing the search in place of the father/homeowner, and the father/homeowner will not participate at all in the search, then the emissaries say the blessing. [The father/homeowner is not allowed to say the blessing if he will not be participating in the search.] If, however, the emissaries are appointed to help the father in his search, then the emissaries are to be present while the father/homeowner says the blessing over the Bedika. They are to have in mind to be Yotzei with his blessing, and are to answer Amen afterwards. After the blessing, each person checks his designated area, being careful to first check the rooms that are near the house/room where the blessing was said in. The above however is only initially required Lechatchilah. If, however, an interval was made between the blessing of the father/homeowner and the beginning of the search of the emissary, or if the emissary was not present at the time that the blessing was said by the father, nevertheless, the emissaries do not need to say a blessing prior to beginning to search.
Who may be appointed as an emissary/helper? From the letter of the law [one who plans to nullify his Chametz, or already did so] may appoint even a woman, or mature child, to perform the search on his behalf, or to assist him with the search. This refers to a child who has the knowledge and ability to do the search in accordance to all the Halachic requirements. [However, children who have not reached the age of responsibility and knowledge to be trusted to do the Bedika, may not be appointed to check, and their search is invalid even Bedieved.] Nonetheless, despite the above allowance, it is a Mitzvah Min Hamuvchar to Lechatchilah only appoint men over the age of 13 to perform the Bedika. In a case that the search is Biblically required, such as if one did not nullify his Chametz, did not sell his Chametz, and it is already past the 6th hour on Erev Pesach, then it is forbidden to rely on women and children and their search is invalid.
May an emissary recite the Bittul nullification? The Bittul nullification must be said by the father/homeowner. However, if the father/homeowner is not home and he is having an emissary perform the Bedika on his behalf, then they are likewise to nullify the Chametz at the end of their search. See Halacha 14 for the full details of this matter.
Becoming an emissary without knowledge of the owner/father: If the father/homeowner traveled away for Pesach and did not instruct his household members who remained at home to search the home for Chametz, they are nevertheless obligated to clean and search it for Chametz. They are likewise to nullify the Chametz after their search even though they were not appointed to do so.
Every father/homeowner is to personally perform, or at least take part in the Bedika. One may appoint other male household members who are above the age of 13 to help perform the search. All participants of the search are to be present when the blessing is recited, and are to begin their search within an area in close proximity to the blessing. Initially, it is best not to appoint women, or children, to perform the search.
May women today be appointed to help search for the Chametz?
May a gentile be appointed as a Shliach to do the Bedika?
 Admur 432:8
 The reason: As is the rule by all mitzvahs that it is a greater mitzvah for one to do the mitzvah himself then for him to appoint an emissary to do it for him. [Admur ibid]
 P”M 432 A”A 5; Letter of Rebbe in Shaar Halacha Uminhag 2:191 that so is possible implication from Siddur who writes “And he should place his household near him to hear the blessing and then have each one check in his area” thus possibly implying that one should merit others to also do the Mitzvah of the Bedika with him and he does not need to do all the Bedika on his own, as despite that in general we say “Mitzvah Bo Yoser Mibishlucho”, since he will be doing some of the checking, he has already fulfilled this mitzvah of “Yoser Bo…”. [Rebbe ibid]
 Piskeiy Teshuvos 432
 The reason: As the going from one house to another before beginning a mitzvah after saying its blessing is considered an interval [as explained above]. [Admur ibid]
 Admur 432:9; Vetzaruch Iyun regarding an older child who makes their own money and purchases and eats their own Chametz at home, if they may repeat the blessing on their own behalf if it was missed.
The reason: The reason for this is because the emissaries are not obligated in doing the Bedika, and are only doing it in order to exempt the father/homeowner from his search obligation. Since in a case that the father/homeowner himself were to check the areas which the emissaries were appointed to check he would not have to repeat the blessing, being that he had already said the blessing once before, therefore, similarly the emissaries which are doing the mission of their father are not obligated to say the blessing. Nevertheless, Lechatchilah they should not do the Bedika without hearing the father/homeowner say the blessing, as otherwise they are doing a Mitzvah without having a blessing precede their mitzvah. [Admur ibid]
Other opinions: Some Poskim rule that the emissaries have to say the blessing if they made an interval or did not hear it said. [Chok Yaakov, brought in M”B 432:11] Some Poskim thus conclude that if the emissary did not hear the blessing, or made an interval, he should not be sent to search, unless it is a case of need that one cannot do the entire search alone. [M”B ibid]
 Admur 432:10; 437:5
 Admur 437:6
 The reason: As all [Jews] are considered kosher to search for Chametz, and are to be believed to have done so. We do not suspect that they will perhaps do the search lazily and thus not search well and will then lie to [the father/homeowner] saying that they searched properly. The reason for this leniency is because the Bedika is only a Rabbinical command, being the Biblically it suffices alone for one to nullify the Chametz. Therefore, the sages believed even the above people, and said that they are to be trusted to do the search. Now, although whenever there is a Chazakah of Issur we do not believe a child to say that he has fixed the issur as we say in Yorah Deah chapter 127, and thus so too here the child should not be believed being that there is a chazakah of Issur in the house being that it was filled with Chametz throughout the year, nevertheless, the child is believed to say that he destroyed the Chametz, being that it was in his ability to do so, and whenever a child has the ability to take care of the Issur, he is believed as explained in Yorah Deah 127 and 120. [Admur ibid]
 The reason: The reason for this is because doing the Bedika in accordance to all its Halachic requirements takes a lot of trouble/work, and thus there is room to suspect that perhaps [women, slaves, and children] will be lazy and not search well. [Admur ibid]
 Admur 437:6
The reason: Women here are not trusted to perform the Bedika. This is despite the fact that they are believed by Torah prohibitions when they have the ability to avoid the prohibition from being transgressed, such as a Nidah is believed to say that she immersed being that she has the ability to immerse, and similarly she is believed on the slaughtering [of an animal] and on the removal of its forbidden parts, to say that she slaughtered and removed the forbidden parts as is required by Jewish law. In these cases she is believed because she had the ability to slaughter and remove the forbidden parts as is required by Jewish law. Nevertheless, here she is not believed to say that she checked [the home] in accordance to the laws applicable to the search, even though she had the ability to check according to Jewish law. The reason for this is because checking in accordance to all the laws is a great burden, and women are [more] lazy [by nature], and they only check a little and say that they checked well. Therefore, the sages did not believe them [to do the search], unless the search is only Rabbinically required to be done. [Admur 437:6]
 Admur 436:3 “If one left his household members in his house and forgot to command them to search the home, they are nevertheless obligated to search even those rooms which they have not entered any Chametz into after the owner of the house left. Even those rooms which they will not enter at all on Pesach at all, and thus one will not come to eat from any leftover Chametz there that is in them, must be checked.”
The reason: The reason for this is because since the homeowner was obligated to search for Chametz all the rooms which are required to be searched [as explained in chapter 433] therefore those who remain in his home are obligated to exempt him from his obligation, as all Jews are guarantors for each other. [Admur ibid]
 Admur 436:4 “After the household members search for Chametz it is proper for them to also nullify the Chametz, and they should be warned to do so, despite the fact that their nullification does not help much being that the Chametz is not theirs and the owner never commanded them to nullify it, and did not make them emissaries [to nullify it or] to check for it.”
The reason: The reason why their nullification does not help much even though one can assume that the owner desires that those remaining in his home nullify the Chametz for him, is because [in order for an emissary to be able to nullify] the owner must explicitly reveal that he wants it to be done, and if not then the nullification of the emissary is meaningless, as explained in chapter 434. The reason for why they should nullify it despite the fact that their nullification does not help much is because we suspect that perhaps the owner will forget to nullify the Chametz in the place that he is in, as since he is not dealing with searching for Chametz and destroying it, it is probable that he will come to forget to do so, and then the Chametz will not be nullified at all. It is thus better for the household members to nullify the Chametz then it not being nullified at all. It is therefore proper to warn them to nullify it in order to remove oneself from doubt. [Admur 436:4]
 Aruch Hashulchan 437:7; Piskeiy Teshuvos ibid; Teshuvos Vehanhagos 2:214
 The reason: Although we rule that one is not initially to appoint women to perform the Bedika. [432:10] Nevertheless the Poskim write that today the women do search properly, unlike back in the time of the Shulchan Aruch. [Aruch Hashulchan ibid]