Unreachable Chametz-Chametz that is in cracks and crevices of tiles and furniture:
Letter of law: If one cannot remove the Chametz with his hands due to it being stuck under cracks and crevices and the like then it suffices for him to nullify the Chametz before the 6th hour [through saying the Bittul of Kol Chamira], and if he plans to do so he is not required to destroy this Chametz before Pesach. One is not required to undo the floor [or to undo furniture] to remove the Chametz even if he is capable of doing so, and rather the nullification suffices. This applies even if one is able to see the Chametz. [This applies even if there is a Kezayis of Chametz. This applies even if the Chametz is visible.] Thus the Chametz that is in between the deep crevices of one’s floor between the tiles [or in the cracks of one’s table or other furniture], does not need to be removed or destroyed but is to merely be nullified. [If one did not nullify his Chametz and did not sell it before Pesach then he must destroy this Chametz on Pesach upon remembering even if it entails taking apart the furniture and the like.]
Yisrael Kedoshim Heim-Custom: All the above is from the letter of the law, however practically the Jewish people are holy and hence the custom is to destroy all Chametz that is in one’s possession, even the Chametz found in unreachable areas. One is thus to pour bleach or other spoiling agent over Chametz that he is unable to reach with his hands. [There is however no basis to extend this stringency to require the taking apart of the item in order to reach the Chametz.]
Chametz that is stuck in a deep hole or crevice and cannot be reached with one’s hands, is not required to be removed and it suffices for him to nullify the Chametz before Pesach. This applies even if there is a Kezayis of visible Chametz found in the crevice. Nonetheless, practically, the Jewish people are holy and destroy all Chametz that is in one’s possession, even if the Chametz found in unreachable areas. Thus, when possible, one is to pour bleach or other spoiling agent over Chametz that he is unable to reach with his hands.
Must one remove Chametz that is stuck in moveable items and can fall out through shaking?
Chametz that is stuck inside a moveable item but cannot be reached by hand, seemingly must be shaken out if one is able to do so. If however, one is unable to shake out the Chametz then it has the same status as any unreachable Chametz, of which we rule nullification suffices, and at the very most spilling a spoiling agent over it. Likewise, this only applies by a Kezayis of Chametz, or less than a Kezayis that is not dirty, if however the Chametz stuck inside is less than a Kezayis and is dirty, then even shaking is not required, as explained in other Halachos.
Does one have to use toothpicks and the like to remove Chametz from areas that he cannot manage to remove with his hands, such as in a fridge?
No. However, by a fridge and other items used with food, one is required to do so in order so Chametz does not Chas Veshalom come to fall into one’s food. In any event, Yisrael Kedoshim Heim and it is thus proper to pour a damaging agent, such as bleach onto the Chametz in all cases that one is able to do so.
Must one remove his car seats in order to remove the Chametz that is stuck under them?
All Chametz that is found under the car seat and is reachable by hand must be removed. All Chametz that cannot be reached by hand is not required to be removed even if one is able to see it. There is no obligation to remove the car seats in order to reach Chametz that is stuck under it. One is likewise not required to vacuum out unreachable Chametz. Nevertheless, practically, experience dictates that it is very difficult to remove even the reachable Chametz [due to abundance of crumbs] without either using a vacuum or removing the car seats. Likewise, in light of Yisrael Kedoshim Heim, Chametz that remains visible and unreachable under the car seat one is to pour bleach or another spoiling agent over it, although is not required to remove the seat.
Must one undo his chair if he sees Chametz in-between the crevices of the cushion and the chair?
This follows the same ruling as the previous Q&A. Thus, all the Chametz that is reachable by hand [or that can be shaken out] must be removed. All Chametz that cannot be reached by hand [and cannot be shaken out] is not required to be removed even if one is able to see it and one is not required to undo the chair in order to remove it. Nevertheless, if there is Chametz that remains visible and unreachable under the cushion, it is proper, if doing so will not damage the cushion, to destroy it by pouring bleach or other spoiling agent over it. If however the Chametz stuck inside is less than a Kezayis and is dirty, then even shaking is not required, as explained in other Halachos.
Must one undo the keyboard of his computer to remove the Chametz stuck under the keys?
No. This applies even if one knows for certain that there is Chametz found there. Nevertheless, in light of Yisrael Kedoshim Heim, those who desire to be stringent and undo the keyboard are not to be protested. In any case that a thorough cleaning was not done, it is strongly advised not to use the same keyboard on Pesach as that used during the year, as it is possible for Chametz to get onto one’s finger and end up in one’s food or mouth.
 433/19; based on 433/21 regarding a hole in wall, 433/30 regarding a Mapoles and 438/11 regarding a pit; Rambam and Michaber 438/2 regarding a pit; Chok Yaakov 433/13; Ashel Avraham 433 according to Rambam; Olas Shabbos 433, although concludes with Tzaruch Iyun because of ruling of Bach; Peri Chadash 433; Makor Chaim 8; M”B 433/29; Implication of P”M 433 A”A 11; Kaf Hachaim 433/56; Piskeiy Teshuvos 433/4
Background from Admur:
Chametz found in the cracks of a wooden plank floor [433/19]: If one has a [floor which has small deep crevice’s in between the tiles, such as by a] wooden board floor with small deep cracks in between the planks of wood, and one is thus unable to enter his hand into the hole to check for Chametz, he does not need to remove the tiles/wood in order to allow him to check under them. Even if one sees that Chametz has fallen into one of the small holes, and if one does not remove it from there, then it will be there throughout all the days of Pesach, nevertheless we do not trouble him to remove it from there, and rather he is to nullify it and that suffices.
Chametz is inside hole of wall[433/20]: The same law applies by a hole in one’s wall or floor which is wide enough for one to fit his hand in, but is very deep, that one is not able to enter his hand to search the entire hole for Chametz, then one checks the hole to as deep that his hand reaches, and the remaining area suffices with ones nullification. This applies even if there is certainly Chametz there [and even if there is more than a Kezayis].
The source of Admur’s ruling: This case ruling of Admur ibid is not recorded in previous Poskim. Admur ibid learned this ruling from the ruling he brings next in 433/21 [as rules Michaber 433/7 and Pesachim 8a] regarding Chametz that is found in a whole in the wall that cannot be reached, in which case we rule that one is not required to check the hole past the area that one can reach with one’s hand, and that this applies even if there is certainly Chametz there. This itself [that even by certain Chametz one is not required to remove it from a deep hole] is learned from 438/11 regarding Chametz found in a pit, in which case we rule that it may remain there over Pesach with Bittul. [Admur ibid; Michaber 438/2; Tur 438; Rambam Chametz 2] [Kuntrus Achron 433/4] It is likewise learned from the ruling in 433/30 regarding a Mapoles of three Tefachim, that even according to the second, stringent opinion, nullification suffices. Thus, in total the basis of Admur’s ruling is from the ruling brought in Michaber ibid regarding a pit, and the ruling regarding a Mapoles, which is the understood ruling regarding a hole in the wall, and hence the same applies to a crack.
Other opinions: Some Poskim rule that if one knows for certain that there is Chametz found in a hole, then he must destroy the Chametz even if it is not reachable by hand, and relying on Bittul does not suffice. [Bach 433; Raavad regarding the law by a pit, brought in Taz 438/4, Chok Yaakov ibid, Ashel Avraham ibid, P”M 433 A”A 11] The Chok Yaakov and Ashel Avraham ibid negate this ruling of Bach, as the Rambam, Tur and Michaber 438/2 all rule unlike the Raavad regarding a pit.
 The reason: The reason for this is because the main enactment of the sages for one to search for Chametz, despite having nullified it, is due to a decree that one may come to eat it on Pesach. Now, in the above case being that this Chametz is in an area which one cannot place his hand in, certainly he will not come to eat it on Pesach. [433/19] Now, although by a Mapoles of less than three Tefachim the Sages nevertheless required one to destroy the Chametz [Admur 433/30], this is only because the Chametz may come to be revealed by a dog through the dog removing the mound. However, here, by Chametz stuck between cracks or in a deep pit, there is no possibility for a dog to undo the wall, or for it to happen on its own, as is common by a mound. There is also no need to suspect that an item of value may get lost in the crack over Pesach and he may come to undo the floor on Pesach in order to retrieve it, as this law is learned from Chametz found in a pit in which case we do not suspect for such a matter. There is also no need to suspect that a rat will remove the Chametz to a reachable area the same way we do not suspect regarding a pit. The reason we do not suspect for a rat dragging out Chametz is because there is no end to such a suspicion. If we were to suspect for such a thing then we should not allow Chametz of a gentile to be kept behind a Mechitza, and should continuously suspect perhaps Chametz in a gentiles house was brought to the house of a Jew. [Kuntrus Achron 433/4]
 See Kaf Hachaim
 Pashut, see Admur ibid in all sources and Kuntrus Achron 433/4; Unlike Piskeiy Teshuvos 433 footnote 6 who says its implied from Admur in Kuntrus Achron ibid that if the Chametz is visible it should be destroyed. This is inaccurate. Upashut!
 Pashut! See 433/30 regarding a Mapoles
 Admur 442/30 and Michaber 442/6 “If there is Chametz in a crack that one cannot remove, then one can place on it a little bit of cement over it”. Now, although one can argue that the above refers to dough that is stuck in the crack of a wall, and bits and pieces can be removed, but its difficult to remove in entirety, nonetheless the spirit of the stringency should apply in this case as well. Vetzaruch Iyun why Admur made no mention here in 433/19 of this matter.
 This is derived from the ruling in Admur 3438/11 which requires one to remove Chametz from a high surface, lest it fall on Pesach and one come to eat. Thus, seemingly, the entire allowance brought above in 433/19 regarding unreachable areas is in a case that the Chametz cannot come to fall out on its own. If however it is possible for it to fall out on Pesach then one should be required to do so. However, this only applies by a Kezayis of Chametz, or less than a Kezayis that is not dirty, if however the Chametz stuck inside is less than a Kezayis and is dirty, then even shaking is not required.
 This is derived from the fact that Admur ibid does not require one to use means other than his hands to remove the Chametz, and if his hands cannot remove it the nullification suffices. Accordingly, one does not need to use toothpick and the like to remove Chametz from cracks, if they are not reachable with one’s hands.
 As since the moving of the fridge door can cause Chametz to fall out from the area that it is stuck in, it is similar to Chametz which is on a high surface which one must remove.
 As explained in the above Halacha from 433/19-20
 Although this is not required from the letter of the law as explained above, nevertheless “Yisrael Kedoshim Heim” and are thus accustomed to destroy all Chametz, even Chametz that is allowed to remain throughout Pesach. Hence one should spoil the Chametz through pouring bleach on it.
 As a) The Chametz is unreachable by hand, and thus nullification alone suffices. b) The Chametz found there is less than a Kezayis and is certainly dirty. Due to the second reason, it is not required to even shake out the Chametz, if possible.
 See Michaber 442/6