How do non-invasive current sensors work?

Question

Electronics

I thought about making a "power meter" purely out of curiosity, but google shows only examples from the series "take this sensor from eBay for $ 10 and plug it into arduino", I somehow don't want to wait 3 months until this sensor arrives "by Russian mail" , tried to google their principle of operation, found nothing. As far as I understand, there is actually something like a transformer that removes charge from the electromagnetic field around the wire and, accordingly, the higher it is, the higher the current, that is, in fact, it can be assembled from a piece of wire and a pair of resistors, but I haven’t found circuits anywhere, can someone share knowledge or kick in which direction can you google?

Answer 1

All the fun is that the power for an arbitrary load cannot be measured with a single current sensor. In addition to current, voltage is needed. You can, of course, try to remove it by the capacitive method, if the current is alternating, but such a sensor will show, rather, the weather on the moon.
"Invasive" wattmeters are more reliable and accurate, but if the load is "simple" (active, known resistance) or the voltage is set, then it is possible with a hall sensor (constant, variable) and a current transformer (only variable), although not so accurately.

Answer 2

Also note that the non-invasive sensor must be hung on one of the wires. This narrows the scope, just splitting the cable into wires is at least disturbing the appearance of the cable.