You are being watching from inside your own blood. A prototype has been developed:
At the upcoming ILSI-Biomed Israel 2009 conference (June 15-17 in Tel Aviv), researchers from the Medical Robotics Laboratory at the Israel Institute of Technology (Technion) will be showing off a microrobot called ViRob, that has only a 1millimeter diameter and can crawl through vessels and cavities, when controlled by an external magnetic field. The big idea behind the ViRob device is that it can be used to deliver pharmaceutical payloads to precise locations or pull a microcatheter through tortuous terrain.
Link and photo via medgadget.com.