There is something to this, but I agree it's mostly BS in how it's being reported here. They can use spectral analysis to correlate different heart beats, as this is what these wearables do. But, to identify each and every person they'd need a recording of their heart beats and I highly doubt they have all this information. Mabey they can get a correlation difference in a lab, but to do this for 7billion people they'd need an awfully large database. Not to mention that peoples heart beats change under various conditions. If they start trying to use this for certain legal things, I suspect the whole idea will go the way of bite marks ... in that it turns out they can't really correlate things as well as they think. And, as you state the only way it could be used to really work would have to under majorly controlled conditions like standing in a certain spot and what not.