When a home security system is necessary for protection against thieves, there are two possible ways to set it up in a halakhically acceptable fashion. The best way is to use a timer. One may set the timer to arm the system during the hours when people are in bed or out of the house and disarm the system during the hours when people are awake and going in and out of the house. The problem with this is that if schedules change, the system needs to be changed, and if doing this involves using electricity, it is absolutely forbidden on Shabbat. If the system has an external timer, one may extend the current state, as explained above (section 6; under pressing circumstances one may also shorten the time, as explained in n. 7).
The second possibility is to use a special key that works via grama. Such a key disarms the security system when turned in one direction and arms it when turned in the other direction. To avoid transgression, the key must not cause any immediate electrical activity. Rather, it activates a mechanism that will eventually activate or disconnect electricity powering the alarm. Even though performing melakha through grama is normally prohibited le-khatĥila, when the only alternative will result in loss, one may be lenient.
Another question regarding security systems relates to monitoring services. In many cases, if a burglar alarms for a home or a car is triggered, the system signals a central monitoring station. Operators at the station see the signal and contact the owner to find out what happened. If the owner does not answer, the operators dispatch security personnel to apprehend the thieves. May one maintain a security system that involves such a service?
Some are stringent and require the owner to demand that the monitoring service refrain from desecrating Shabbat on his behalf. This approach would require the service to use non-Jewish security personnel on Shabbat. Others permit using a monitoring service even if it is staffed by Jews, maintaining that every theft nowadays involves an element of danger to human life. Therefore one may hire a service that employs and sends out Jewish security personnel on Shabbat. In practice, it is proper to use a company that tries to use non-Jewish security personnel on Shabbat. If that is not an option, one may use a company that is not particular in this regard. If the alarm goes off and the service calls to find out if a dispatch is necessary, even if the personnel are non-Jews, one should answer the phone, in order to prevent them from making an unnecessary trip.
. Within this second possibility, there are two permissible options. The first is to set it up so that when the system is shut off via grama, all the sensors stop working, and when it is re-armed the sensors resume working. The advantage of this option is that while people are home, no sensors are activated. The disadvantage is that every turn of the key causes the electrical system to turn on or off. The second option is to arrange that the sensors are always working, while the key simply serves to connect and disconnect the alarm system. The disadvantage of this option is that every movement in the house activates the sensors (see the previous section). The advantage is that turning the key does not cause any recognizable electrical activity. Even when the system is armed, if no thief enters, the alarm will not go off.
. Orĥot Shabbat 23:208 maintains that one may not hire a security service that is under Jewish ownership or hires Jewish workers. In contrast, R. Shaul Yisraeli (Amud Ha-yemini §17) maintains that police may take action against thieves on Shabbat because it prevents danger to human life. Be-mar’eh Ha-bazak 4:43 applies this approach to monitoring services as well. Nowadays, there is an additional reason to be lenient. Thieves in Israel are often connected with terrorists. Just as the Sages allowed people in border towns to defend themselves on Shabbat against robbers of straw and hay (SA 329:6), so, too, people who live anywhere in Israel may defend themselves against the thievery of terrorists (below 27:12). In practice, one should give preference to a monitoring service that tries to hire non-Jewish guards. Nevertheless, this is not absolutely necessary, because the primary position is that preventing theft involves preserving lives as well. Not only that, but one may answer the phone when the monitoring service calls to check if there was a break-in. This is similar to the case of ambulances, which we discuss in 27:10 below. All false alarms cause danger to human life. See Harĥavot.
Connecting a synagogue ark to an alarm system and disconnecting it when the Torah scrolls are taken out to be read must be done by means of grama, that is, using a key that activates or deactivates the system only a few minutes after the key is turned. In Teĥumin 1, Rav Dasberg proposed an excellent solution that does not even require grama. See Harĥavot.