Sensors are the primary components of a monitoring system. Micro- and nanofabrication technologies have now advanced to the stage at which wireless sensor systems can be included in the implants with minor modification. These systems provide unique, personalized data for each patient to be used for optimizing outcomes. An acceleration sensor mounted on an artery is used for blood pressure measurement. Coupling a pressure transducer to the right ventricle (RV) lead of a pacemaker or defibrillator helps in continuous intracardiac pressure monitoring. Implantable chemical sensors are employed for real-time monitoring of clinically important species, e.g., blood gas measurements (pH, pO2, and pCO2). Subcutaneously implanted enzymatic glucose sensors enable continuous glucose monitoring. Single-walled carbon nanotubes (SWCNTs) encased in alginate work as inflammation sensors, which can be implanted for detection of nitric oxide.