A system comprising: at least a portion of a communications bus; at least one electronic control unit, ECU, electrically coupled between a plurality of nodes and the portion of the communications bus; at least one security module comprising at least one data processor, the at least one security module electrically coupled to the at least one ECU and the portion of the communications bus; and memory-storing instructions, which when executed by at least one data processor result in operations comprising: monitoring, by at least one data processor of at least one security module, a plurality of voltage lines of at least one electronic control unit, ECU, electrically coupled to a communications bus, the communications bus comprising a serial communications bus, wherein serial communications bus comprises a controller area network bus and wherein the at least two of the plurality of voltage lines comprises either a CAN high voltage line or a CAN low voltage line and a ground line; measuring, by at least one data processor, a voltage differential across at least two of the plurality of voltage lines of the at least one ECU; comparing, by at least one data processor, the voltage differential to a plurality of predetermined signal fingerprints associated with the at least one ECU; identifying, by at least one data processor and based on the comparing, a variance in the compared voltage differential relative to one or more of the plurality of predetermined signal fingerprints; and providing, by at least one data processor, data characterizing the identified variance, wherein information is encoded by the at least one security module and injected into the CAN bus using low voltage pulses relative to CAN bus ground. at least a portion of a communications bus; at least one electronic control unit, ECU, electrically coupled between a plurality of nodes and the portion of the communications bus; at least one security module comprising at least one data processor, the at least one security module electrically coupled to the at least one ECU and the portion of the communications bus; and memory-storing instructions, which when executed by at least one data processor result in operations comprising: monitoring, by at least one data processor of at least one security module, a plurality of voltage lines of at least one electronic control unit, ECU, electrically coupled to a communications bus, the communications bus comprising a serial communications bus, wherein serial communications bus comprises a controller area network bus and wherein the at least two of the plurality of voltage lines comprises either a CAN high voltage line or a CAN low voltage line and a ground line; measuring, by at least one data processor, a voltage differential across at least two of the plurality of voltage lines of the at least one ECU; comparing, by at least one data processor, the voltage differential to a plurality of predetermined signal fingerprints associated with the at least one ECU; identifying, by at least one data processor and based on the comparing, a variance in the compared voltage differential relative to one or more of the plurality of predetermined signal fingerprints; and providing, by at least one data processor, data characterizing the identified variance, wherein information is encoded by the at least one security module and injected into the CAN bus using low voltage pulses relative to CAN bus ground. monitoring, by at least one data processor of at least one security module, a plurality of voltage lines of at least one electronic control unit, ECU, electrically coupled to a communications bus, the communications bus comprising a serial communications bus, wherein serial communications bus comprises a controller area network bus and wherein the at least two of the plurality of voltage lines comprises either a CAN high voltage line or a CAN low voltage line and a ground line; measuring, by at least one data processor, a voltage differential across at least two of the plurality of voltage lines of the at least one ECU; comparing, by at least one data processor, the voltage differential to a plurality of predetermined signal fingerprints associated with the at least one ECU; identifying, by at least one data processor and based on the comparing, a variance in the compared voltage differential relative to one or more of the plurality of predetermined signal fingerprints; and providing, by at least one data processor, data characterizing the identified variance, wherein information is encoded by the at least one security module and injected into the CAN bus using low voltage pulses relative to CAN bus ground.