Adapting modern technology to ancient halacha, or Jewish religious law, is a challenge that Israeli experts have long relished. But the "Shabbat phone" is in a class of its own.
Orthodox Jews do not make or receive phone calls on the Sabbath ("Shabbat" in Hebrew), as the activation of an electric appliance - so that a current is introduced to a device - violates rules against starting or completing a project on the day of rest.
This has posed a problem for key senior military officers and public servants, who are observant or modern orthodox Jews but need to be on call 24/7.
The Shabbat phone, from the Zomet Institute, has been dubbed kosher as the current continuously runs through it, and increases when the call is made.
Twelve Shabbat phones were ordered six months ago for religious personnel among Prime Minister Benjamin Netanyahu's staff.
But Zomet head Rabbi Yisrael Rosen said the "halachic approval was only given for essential workers and important needs like health, security, public services, water and electricity".