[howardr]

One of my friends said that his grandparents would light their stove before sundown on friday and leave it lit until sundown Saturday so they would not break kosher laws

I have also heard that a lot of devices have kosher mode. E.g. refrigerators lights not coming on and power randomly going in and out much like this swith

[_delirium]

The random-refrigerator-compressor one is something I read about recently and would never have occurred to me. The reasoning is that in a normal setup, the compressor's operation is driven by internal temperature, which is impacted by opening/closing the door, so opening/closing the door is indirectly "operating" an electric motor, the compressor. To avoid that, in Sabbath mode the compressor runs on a non-thermostat-based schedule, so its operation is not being directed by any human activity.

Some electric ovens and stoves also have a Sabbath mode that lets them stay on all day; in the normal mode most have an auto-shutoff after 12 hours, under the assumption that an oven left on for more than 12 hours was probably an accident.