The OBS consists of a signal conditioner (which requires two batteries), an intravehicular activity (IVA) cable, an electrode harness, and the signal conditioner belt.
The signal conditioner has two connections: the first goes to the electrode harness, which is attached to the crew member via electrodes, and the second goes to the IVA cable, which in turn connects to the Orbiter BIOMED cable, which plugs into the Orbiter at the MS BIOMED jack on panel A11 or the PS BIOMED jack on panel A15 for data download.
Three electrodes are placed on the skin. Each of them connects to the amplifier through an electroshock protection (ESP) circuit. The electrodes detect the moving electric field generated by heart muscle depolarization and repolarization. This electric field is amplified and conditioned by the signal conditioner. There is no ON/OFF switch for the signal conditioner; the unit is activated when output connectors are mated.