Every Friday night, as Shabbat starts in Jay and Lauren Hofstatter’s home in Boca Raton, Fla., all televisions automatically shut down, ground-floor lights come on and bedroom lights switch off. A cozy home theater, closed off during the week, is programmed to unlock—not for watching television but for family time after the evening meal.

The system will respond when Yom Kippur, the highest Jewish holiday, begins on the evening of Oct. 8. Linked to a cloud-based Hebrew calendar, it will set lighting and electronics to a “no...