A defibrillator system comprising: a defibrillator (100, 410) including: an energy storage device (350, 415) configured to store an electrical charge; a defibrillation port (310, 420); a display; a defibrillator processor configured to control the display and when an electrical charge is applied to the defibrillation port for defibrillating a patient; a defibrillator data connect port; and a first utility module (455, 700, 1608, 1800) configured to be carried with the defibrillator (100, 410) to a location of the patient, including: a parameter module configured to detect a parameter of a patient; a data outlet configured to engage the defibrillator data connect port to enable transmission of data to or receipt of data from the defibrillator (100, 410); and a module processor configured to control the parameter module and to control communications between the defibrillator (100, 410) and the parameter module that include the transmission of data from the utility module (455, 700) to the defibrillator (100, 410) and configured to execute an instance of an event service that provides data communications between the utility module (455, 700) and one or more external devices. a defibrillator (100, 410) including: an energy storage device (350, 415) configured to store an electrical charge; a defibrillation port (310, 420); a display; a defibrillator processor configured to control the display and when an electrical charge is applied to the defibrillation port for defibrillating a patient; a defibrillator data connect port; and an energy storage device (350, 415) configured to store an electrical charge; a defibrillation port (310, 420); a display; a defibrillator processor configured to control the display and when an electrical charge is applied to the defibrillation port for defibrillating a patient; a defibrillator data connect port; and a first utility module (455, 700, 1608, 1800) configured to be carried with the defibrillator (100, 410) to a location of the patient, including: a parameter module configured to detect a parameter of a patient; a data outlet configured to engage the defibrillator data connect port to enable transmission of data to or receipt of data from the defibrillator (100, 410); and a module processor configured to control the parameter module and to control communications between the defibrillator (100, 410) and the parameter module that include the transmission of data from the utility module (455, 700) to the defibrillator (100, 410) and configured to execute an instance of an event service that provides data communications between the utility module (455, 700) and one or more external devices. a parameter module configured to detect a parameter of a patient; a data outlet configured to engage the defibrillator data connect port to enable transmission of data to or receipt of data from the defibrillator (100, 410); and a module processor configured to control the parameter module and to control communications between the defibrillator (100, 410) and the parameter module that include the transmission of data from the utility module (455, 700) to the defibrillator (100, 410) and configured to execute an instance of an event service that provides data communications between the utility module (455, 700) and one or more external devices.