Constructing a mikveh by permanently fixing at least one initial building unit to the ground of an installation site, connecting, in a sealed manner, additional building units to the initial building unit, for producing a sealed vessel, where the length of each of most of said building units is at least 50 centimeters, and the weight per area thereof is less than 250 kg per square meter. The method includes: a base station and its neighboring base station encapsulating and transmitting the energy-saving management information through an interface message. The gun has means for notifying remote authorities that the gun has been removed from the holster, means for receiving remote commands to lock the trigger andor initiate a global positioning system.