Communication method and system for bidirectional data transfer among smart modules (101-111) attachable to a weapon (100), where messages are encoded by modulating an electric supply provided by at least one powered rail (200, 200′, 200″, 200′″). At least two priority levels are defined among smart modules supplied by the powered rail (200, 200′, 200″, 200′″). High-priority smart modules (600) are allowed to transmit high-priority data message (741) directly; whereas low-priority smart modules (500) are required to transmit a data transfer request message (723) and wait for a data transfer permission message (731), which is only sent when no high-priority data message (741) is being received.