NOVELTY - The in-body power source e.g. batteries and capacitors useful in implantable and ingestible devices to emit a detectable signal upon contact with a target physiological site, comprises a solid support (120), a first high surface electrode, and a second electrode, where the electrodes are present on a same or opposite surface of the support. The solid support has a semiconductor material and an integrated circuit. The first high surface electrode is a cathode (160) or an anode (180). The high surface area electrode has an active electrode material (170), which is present on a porous electrode under-layer (150).    USE - The in-body power source is useful to emit a detectable signal upon contact with a target physiological site (claimed), where the power source is batteries and capacitors present in implantable and ingestible devices for diagnostic and therapeutic functions.    ADVANTAGE - The in-body power source is compact and easily handled with implantable and ingestible medical and related technologies, and effectively provides automatic detection and identification of pharmaceutical agents delivered into the body.    DETAILED DESCRIPTION - The in-body power source e.g. batteries and capacitors useful in implantable and ingestible devices to emit a detectable signal upon contact with a target physiological site, comprises a solid support (120), a first high surface electrode, and a second electrode, where the electrodes are present on a same or opposite surface of the support. The solid support has a semiconductor material and an integrated circuit. The first high surface electrode is a cathode (160) or an anode (180). The high surface area electrode has an active electrode material (170), which is present on a porous electrode under-layer (150). The porous electrode under-layer is electrodeposited, and is produced by cathodic arc and electrophoretic deposition. The in-body power source is present in a pharmaceutically acceptable carrier composition that is a tablet and a capsule. INDEPENDENT CLAIMS are included for:    (1) a system;    (2) a method; and    (3) a kit.    DESCRIPTION OF DRAWING(S) - The figure shows a battery having a porous cathode under-layer.    Solid support (120)    Porous under-layer (150)    Cathode (160)    active electrode material (170)    Anode. (180)