-from the Rabbinical Assembly website.

At nightfall, on the 14th of Nisan, the night before Erev Pesah, it is an obligation to search for leaven.  Although by then the house will have a top-to-bottom cleaning, a thorough search is nevertheless required to ensure that no hametz remains unwittingly in one's possession. Ten pieces of bread are strategically placed in ten locations throughout the home. If there are any children in the home, this will most certainly rouse their curiosity. The bread is then collected during the search, and reserved to be burned the following morning.