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Telephones, Microphones, and Hearing Aids: Even if a phone is already in use before Shabbat, or a microphone is turned on before Shabbat, one may not speak on the phone or into the microphone on Shabbat, because doing so increases the electric current running through them, which is considered like stoking a fire.
Nevertheless, someone hard of hearing may use an electric hearing aid that rests on or inside the ear, because the people speaking to him do not speak into the device. They speak normally and the device is activated indirectly (section 5 above). The hearing aid should be turned on before Shabbat, and the volume should not be adjusted on Shabbat. When the person wants to go to sleep, the device should be removed. In the morning, one may put it back in without turning it on.
Refrigerators: If opening a refrigerator door causes a light to turn on or leads to other electric activity, one may not open the door. Therefore, the refrigerator light should be disabled before Shabbat. To avoid the problem of forgetting to do so, many people simply remove the light bulb permanently and do without it all the time.
Elevators: Using an elevator on Shabbat is forbidden. However, one may use a “Shabbat elevator” which is set to run automatically.
Automatic Doors: It is prohibited to approach a door that opens automatically when it senses a person is near. Someone who finds himself in a hotel with automatic doors must find an alternative way to enter that does not involve using electricity. If a non-Jew approaches the door to enter, a Jew may follow. (Similarly, a Jew may follow a non-Jew into an elevator if they are going to the same floor.)
Security Cameras, Metal Detectors, and Motion Detectors: A person may walk in a place where security cameras record videos of passersby, since one has no interest in being videoed. Similarly, a person may pass through a metal detector, since one is not interested in its electrical activity, and this activity is automated. A person may also walk on a street where there are motion detectors which turn on lights, because one is innocently walking through and is not interested in turning on the lights. However, a person must disable a light which automatically turns on in front of one's own home. Since it is set up to provide family members and guests with light, anyone walking there is considered to be intentionally turning on the light.
Sensors: A person may walk in a building where the security system has been disabled but the sensors continue working, even if this means LED security lights go on or images are recorded whenever one passes by certain places. Nevertheless, it is preferable to disable the sensors too, if possible.
Security Systems: When a home security system is necessary for protection against theft, there are two possible ways to set it up in a halakhically acceptable fashion. The first is to use a timer that will arm the system only after everyone has gone to bed. The second is to use a special key (produced and supplied by halakhic institutes for this purpose) that works indirectly. Instead of immediately activating or deactivating the system, these keys only affect the system after a delay of approximately ten minutes. We have already seen that in cases of great necessity, it is permissible to do melakha indirectly.
Alarms: If someone accidentally triggers a car or home alarm on Shabbat, what should be done? If it is during the day, and the alarm will stop relatively soon and will not disturb people for long, one may not take any action to turn it off. However, if it will continue making noise for a long time by day or even a short time at night, the alarm may be turned off with a shinui (such as using the back of the finger to press the appropriate button). This is because while lighting a fire is prohibited biblically, extinguishing it is only prohibited rabbinically. When extinguishing (or turning off the electricity) is done with a shinui, this makes the prohibition even less severe. The Sages permitted taking such actions to prevent suffering.
