Saying an abridged version of Kerias Shema Sheal Hamitah on the 1st night of Pesach:[1]

 [On the 1st night of Pesach] one only recites the first paragraph of the Shema and [then goes straight to] the blessing of Hamapil.[2] If, however, one Davened Maariv in Shul prior to nightfall, then he is to repeat and read all three paragraphs on his bed. [On the 2nd night of Pesach, however, one recites the regular paragraphs as is said on every Yom Tov.[3]] [The blessing of Hamapil may be recited even after midnight[4], although may no longer be recited after Alos Hashachar.[5]]

______________________________

[1] Admur 481:2; Rama 481:2 regarding Parshas Shema; Mahariy Viyal 193 in end; M”A 481:2; Chok Yaakov 481:7; Elya Raba 451:3; Kitzur SHU”A 119:9; Chayeh Adam 130:16; M”B 481:4

Other opinions: Some Poskim rule that according to Kabballah one is not to say the blessing of Hamapil on the night of Pesach. [Kaf Hachaim 481:14 in name of Arizal in Shaar Hakavanos Pesach 3] Some Poskim rule one is to recite Kerias Shema as usual, with all three paragraphs of Shema and the other verses usually recited. [Ben Ish Chaiy Tzav 38; Kaf Hachaim 481:13]

[2] The reason: The custom by bedtime is to only read the blessing of Hamapil and the paragraph of Shema, and not the other paragraphs that are customarily recited on the other nights for the sake of protection. The reason for this is because the [first] night of Pesach is guarded from damaging forces [by Hashem, and there is thus no need to recite the paragraphs recited for protection]. [Admur ibid; Rama ibid; Pesachim 109b] However, one does recite the first paragraph of Shema and Hamapil, as they are mentioned in the Gemara Brachos 60b. [Admur ibid; M”A ibid]

[3] Sefer Haminhagim p. 42; Vayaged Moshe 33:8; See Piskeiy Teshuvos 481:2

Other customs: Some recite an abridged version of Kerias Shema Sheal Hamita also on the 2^nd night. [P”M 481 A”A 2 in name of Levush]

[4] Conclusion of Birkeiy Yosef 239 in name of Lachmei Toda; Shaareiy Teshuvah 239:1; Biur Halacha 239:1 “Samuch”; Ashel Avraham Butchach 239; Kuntrus Alei Terufa; Darkei Chaim Veshalom 348; Keren Ledavid 60; Hisorerus Teshuvah 1:115; Meishiv Halacha 419; Binyan David 29; Teshuvos Vehanhagos 1:198; Piskeiy Teshuvos 239:2

Other opinions: Some Poskim rule one may not recite the blessing after midnight. [Opinion brought in Birkeiy Yosef 239 in name of Lachmei Toda, brought in Shaareiy Teshuvah 239:1; Chesed Lealafdim 239:10; Rav Poalim 1 Sod Meisharim 14; Kaf Hachaim 239:8 based on Shaar Hakavanos; Custom of Jerusalem in Yeshivas Hamekubalim Beis Keil; Yechaveh Daas 4:21 that Safek Brachos Lihakel] Practically, while the widespread custom is to say Hamapil with a blessing even after midnight, some are particular to say it without a blessing.

[5] Biur Halacha ibid; Ashel Avraham Butchach 239; Keren Ledavid 60; Hisorerus Teshuvah 1:115; Meishiv Halacha 419; Binyan David 29