We have a number of mishmar ezrachi volunteers in our Jerusalem shul, and occassionally we are contacted by the police before chagim regarding terrorist warnings, with the advice that our volunteers guard the shul. Is there any problem with the following: carrying the gun and ammunition to shul; missing services because we are outside guarding; carrying a cell phone in case of emergencies; or any other issue you can think of. Thank you.
The chief Rabbinnate of the police has a detailed instruction sheet on what is allowed and forbidden, I suggest you ask for it. Regarding your questions - in the case of an emergency or possibility of an emergency all the problem you asked about are permitted. Rabbi Yitzchak Grinblat