Medical equipment is expensive and not always accessible to a wide audience. In fact, in any biomedical measuring instrument there is nothing extraordinary – here you can find ADC, analog front-end with low noise op-amp, some controller. But the central part what makes it different from consumer electronics is safety. Because device is connected to your body through some sort of electrodes, there is always a risk of electric shock. So power supply has to be isolated if it is powered from mains. There might be other additional safety circuitry to prevent possible hazard. And of course there are many safety regulations and certificates to overcome before device can be used with patients. This is where main cost comes from. It doesn’t mean that you cannot experiment with your body signals. You only need to know what are you doing. If you are building your circuit to acquire bio-signals, be sure to use a proper isolated power supply, even better – go with battery power. Once said, let’s look at great development of Arduino shield to be used for acquiring various bio-signals from your body.