Defibrillation is a treatment for life-threatening cardiac arrhythmia, or irregular heart beat. A portable defibrillator is a device that delivers an electric current to the heart, when cardio-pulmonary resuscitation, or CPR is required. Defibrillators can be external or battery powered or implantable. Some models of external defibrillators come with a battery to make this devices portable for use in ambulances and other reserved zones. These need to conserve battery to ensure the high current discharge that is required. This is where special high voltage reed switches, capable of switching thousands of volts are used by assembling into High Voltage Reed Relays. These relays are triggered by a button the person in charge of CPR presses, when the set power has been reached. Implantable versions are known as cardioverter-debrillators and are inserted into the body using a procedure similar to that of pacemaker insertion. This type of debrillator maintains irregular heartbeats by pacing the heart and giving high or low level currents as and when required. Implants use ultra-miniature reed sensors to help change the mode of operation by using an external magnetic wand.