111:7 Before one starts to search for chometz, he recites the bracha al bi’ur chometz, that G-d has commanded us to remove chometz. He recites this bracha even though he is not yet removing the chometz because immediately after the search, he nullifies any chometz that he may not know about, which constitutes removing that chometz. One should not interrupt between reciting the bracha and starting the search. (If one interrupted with irrelevant conversation, he must repeat the bracha – Mishnah Brurah 432:5.) Preferably, one should not interrupt until he has finished the search, except for something relevant to performing the search. (If one interrupted mid-search, he need not repeat the bracha – MB 432:6.) One can check several houses relying on a single bracha. (Walking from house to house does not constitute an interruption – MB 432:7.)
111:8 Many have the practice before the search to put pieces of bread where they will be found by the one conducting the search. This is because of a concern that nothing will be found and the bracha will have been recited in vain. (If nothing is found, the bracha would not be in vain because the obligation is to search for the chometz, even if nothing is found – MB 432:12.) It’s obvious that one who does not search properly and just gathers up those pieces has not fulfilled his obligation to search and has recited the bracha in vain.