These fucks will say something like; >nahh dummy they use the brain to tell!!! When there is ZERO medically or scientifically recognized way to measure brain activity to determine death. Zero. Not even Zero brain electrical signal is equal to dead, people have come back. However so is heart stoppage. I had mine stop quite a few times in a couple minute in the ER. However "heart stoppage" does have a metric to gauge where if it stops, and XYZ things are tried for a period of N time and whatever else and the heart can't be restarted, THEN it's considered dead.