A resuscitation system for use by a rescuer for resuscitating a patient, comprising at least two high-voltage defibrillation electrodes, a first electrical unit comprising circuitry for providing resuscitation prompts to the rescuer, a second electrical unit separate from the first unit and comprising circuitry for providing defibrillation pulses to the electrodes, and circuitry for providing at least one electrical connection between the first and second units. In another aspect, at least two electrical therapy electrodes adapted to be worn by the patient for extended periods of time, circuitry for monitoring the ECG of the patient, an activity sensor adapted to be worn by the patient and capable of providing an output from which the patient's current activity can be estimated, and at least one processor configured for estimating the patient's current activity by analyzing the output of the activity sensor, analyzing the ECG of the patient, and determining whether electrical therapy should be delivered to the electrodes.