Can one use a sand timer on Shabbos?
My children want to say Tehillim on Shabbos Mevorchim and will earn rewards for it. They will earn rewards by the amount of time they spend saying Tehillim. Therefore, the question is, are they allowed to use a sand timer so they can make sure they are reading for the designated amount of time? Using the time on a clock will not be as child-friendly and effective.
Sand timers should not be used on Shabbos, even for a Mitzvah.
The Alter Rebbe writes (Shulchan Aruch Harav 308, 88) that the above is the common custom, although Halachicly it is unclear whether this is prohibited or permissible.