A defibrillator comprising: a high voltage delivery system (13, 16) comprising an energy source and a switch connecting the energy source to electrodes (40, 204) of the defibrillator; a controller (22, 34)) operably connected to the high voltage delivery system; a self-test system comprising: a defibrillator status indicator comprising a fault indicator; a self-test system energy source; conductors in electrical communication with the self-test system energy source; test pads being in electrical contact with the electrodes; means for periodically delivering a test signal through the conductors to the test pads, wherein said means comprise a test signal generator; a patient simulator communicating with the conductors; a test signal analyzer communicating with the conductors and the patient simulator; and the fault indicator communicating with the test signal analyzer; the electrodes (40, 204) being configured to retrieve the test signal; characterised in that the test signal is of at least two types, wherein the at least two types comprise normal patient ECG waveforms and ECG waveforms indicating a therapeutic pulse is required; the test signal analyzer comprises a microprocessor; the microprocessor is configured to indicate a fault on the fault indicator if the test signal is one of the normal patient ECG waveforms and the microprocessor determines that a therapeutic pulse is required, and/or the test signal is one of the ECG waveforms indicating a therapeutic pulse is required and the microprocessor determines that a therapeutic pulse is not required. a high voltage delivery system (13, 16) comprising an energy source and a switch connecting the energy source to electrodes (40, 204) of the defibrillator; a controller (22, 34)) operably connected to the high voltage delivery system; a self-test system comprising: a defibrillator status indicator comprising a fault indicator; a self-test system energy source; conductors in electrical communication with the self-test system energy source; test pads being in electrical contact with the electrodes; means for periodically delivering a test signal through the conductors to the test pads, wherein said means comprise a test signal generator; a patient simulator communicating with the conductors; a test signal analyzer communicating with the conductors and the patient simulator; and the fault indicator communicating with the test signal analyzer; a defibrillator status indicator comprising a fault indicator; a self-test system energy source; conductors in electrical communication with the self-test system energy source; test pads being in electrical contact with the electrodes; means for periodically delivering a test signal through the conductors to the test pads, wherein said means comprise a test signal generator; a patient simulator communicating with the conductors; a test signal analyzer communicating with the conductors and the patient simulator; and the fault indicator communicating with the test signal analyzer; the electrodes (40, 204) being configured to retrieve the test signal; characterised in that the test signal is of at least two types, wherein the at least two types comprise normal patient ECG waveforms and ECG waveforms indicating a therapeutic pulse is required; the test signal analyzer comprises a microprocessor; the microprocessor is configured to indicate a fault on the fault indicator if the test signal is one of the normal patient ECG waveforms and the microprocessor determines that a therapeutic pulse is required, and/or the test signal is one of the ECG waveforms indicating a therapeutic pulse is required and the microprocessor determines that a therapeutic pulse is not required. the at least two types comprise normal patient ECG waveforms and ECG waveforms indicating a therapeutic pulse is required; the test signal analyzer comprises a microprocessor; the microprocessor is configured to indicate a fault on the fault indicator if the test signal is one of the normal patient ECG waveforms and the microprocessor determines that a therapeutic pulse is required, and/or the test signal is one of the ECG waveforms indicating a therapeutic pulse is required and the microprocessor determines that a therapeutic pulse is not required. the test signal is one of the normal patient ECG waveforms and the microprocessor determines that a therapeutic pulse is required, and/or the test signal is one of the ECG waveforms indicating a therapeutic pulse is required and the microprocessor determines that a therapeutic pulse is not required.