A defibrillator system capable of defibrillation and patient monitoring. When used as a patient monitor, the defibrillator system includes a defibrillator and removable monitoring electrodes. The monitoring electrodes communicate with a monitoring adapter and the defibrillator. A method of detecting the presence of the monitoring electrodes by the defibrillator is also included. A removable monitoring adapter. The removable monitoring adapter having a test impedance. Defibrillators include semi-automatic defibrillators and automatic defibrillators ("AEDs").