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.

Who is "we"?

Just some thoughts on this.

If you use the right sonic spectrum, you can hit resonance of a glass and break it. The same idea works for fibrillation and defibrillation, and energy can be attenuated in many ways. For example, the blood in the veins can take attenuation (act as a natural antenna for certain frequencies) which will disrupt the heart. If you get the frequency right you just have to blast a wave at someone's body and it will mess up the flow such that the heart (pump) starts to not work correctly.

Again, there are multiple ways this attenuation can be done: electric field, sonic wave, em-wave (light or "rays"), etc. I don't know the exact details, but I've seen people talking about this since the 1970s in science fiction and other places.

Are they confirmed? Not so much. But, if they had such a thing, those in charge would definitely be pressed to say it didn't exist.

My instinct is that 5G (and the other em radio spectrum) will and have been causing problems for certain people for a long time - at least there have been reports of such things happening. The microwave spectrum (which is what 5G is on) would be able to do this attenuation as it is the right range for liquid molecules (like blood). This is actually how a microwave heats food.