Can human body send any kind of signal to a electrical circuit?
Sure, you can buy sensors that detect body heat to turn something on. Many automatic doors now use passive infrared sensors that watch for body heat moving in their field of view. I’ve found that if I am wearing a hat and coat and keep my head down as I walk into the local post office, the door won’t open unless I look up so the sensor has a view of my face. I also have a beard, which will tend to block body heat from the lower half of my face. As far as electrical signals, any such signals from the human body are so weak that medical equipment designed to detect them require direct connections and some very special electronics designed to be very low noise and cancel outside noise sources. And all medical equipment is designed to give off -very- low EMI so they aren’t interfering with themselves and other equipment. There are other sensors that are active, they look for a large object to either block a beam or to cause a microwave beam to shift frequency. Essentially a low power, low
