Shalom Aleichem! I live in Queens, New York. I would like to know if one is permitted to wear a bulletproof under his short or jacket on Shabbos where there is an eruv. There have been several past instances of gunmen attempting to or actually attacking houses of worship across the USA particularly in todays antisemitic environment. The police have also thwarted many attacks in the planning stages. The shul I daven in during the week has a locked front door with a code to enter but has no security guard on duty. They do, however, have a guard on Shabbos. I, for one, do not feel very safe with this one guard on duty at the front door as it would not take much for a would be armed attacker to incapacitate or neutralize him. If this were to chas vshalom happen, the attacker would be able to then make his way into the main sanctuary unimpeded and chas vshalom do the unimaginable. I am an armed citizen licensed to carry a concealed weapon. However, my request to be allowed to carry my weapon in shul on weekdays and Shabbos/yom tov was denied by the shul president without stating any reason. New York State prohibits the carrying of firearms in houses of worship unless the member has givenauthorized by the house of worship to act as a member of their volunteer security team.

ב"ה Shalom, It seems that perhaps you meant to ask if one is permitted to wear a bulletproof vest under his shirt or jacket on Shabbos where there is NO eruv. If there is an Eruv, there is no problem wearing something, neither is a bullet proof vest Muktzeh. Since a bulletproof vest is worn as a garment, there would be no problem wearing it where there is no Eruv. The same way a person can wear a raincoat even when it is not raining. (See Shulchan Aruch 301: 14.) The bigger problem is carrying a weapon. In regard to Muktzeh there are those who define a gun as a "Kli Shmelachto Leheter" meaning a utensil whose use is for things permitted on Shabbat. Since a weapon creates a situation of deterrence, which is permitted on Shabbat, therefore there is room to be lenient and not to consider a gun Muktzeh, when used for security purposes. [See שולחן שלמה סימן שח ס"ק טז וכז, (ומובא גם בשמירת שבת כהלכתה פ"כ הערה כח),] The main issue is carrying a gun on Shabbat where there is no Eruv. Weapons should not be carried unless there is an operational need. The operational need is determined by the level of Pikuach Nefesh. The fact that many shuls today have armed guards or police cars on the street outside of the Shul during services , seems to indicate that there is a justification for carrying a weapon on Shabbat. However, I think it would be wise to consult with the Rabbi of your shul , how to conduct yourself. Furthermore, if a congregation allows its congregants to bring guns for security, there must be an organized plan in case of emergency in coordination with local law enforcement, so that those carrying firearms do not cause harm before they provide protection. הנה לא ינום ולא יישן שומר ישראל All the best