Q. A person who woke up in the middle of the night on Friday night and, while still half-asleep and not realizing that it’s Shabbos, pressed the button on his watch (which he was wearing) to make it light up to see what time it was, what is the appropriate teshuva for such a person? Maybe not to wear a watch on Shabbos….
Is this shogeg, or more like misaseik, since when a person is sleepy (waking up in the middle of the night), he is almost on the level of a shoteh?

A. See question 1519. Lighting an LED light on Shabbos is at least Rabbinically prohibited. It could also include the Biblical proscription of tikun mono or fixing a vessel.
Horav Shlomo Miller’s Shlit’a opinion is that doing it while half a sleep is not called missassek, it is rather unintentional or shogeg and therefore requires kapara. The Rov recommended to place some tape on the buttons of the watch.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a.