If I go to sleep at night and unexpectedly wake up after alos ha’shachar and wish to go back to sleep, is there halachically anything that needs to be done before going back to sleep (e.g. kerias shema)? If I have an alarm that is set to go off later in the morning to wake me up for Shacharis, would that make a difference?
Before going back to sleep make sure there is someone who can wake you up, so that you don’t miss zman kriyas shema. According to many poskim an alarm clock is considered a shomer, to wake you up. It is advisable not to put the alarm clock too close to you, because you might just shut it off in your sleep, and then it sdoesn’t really help you much.
Additionally, it is a good idea to saying the posuk of Shema and Boruch shem before going back to sleep, just in case you oversleep.
Dinim V’hanhagos Chazon Ish chap. 4-4, Eishei Yisroel 13-31. Rema O:CH 46-8, also see Mishna Berura 46-31 there that it is even better to whole first parsha, and according to some all three.