To my knowledge, a hall effect sensor is just a soft-cored hooped metal (iron?) with some wire wrapped around it a precise number of turns. This surrounds another wire that you wish to measure the intensity of passing current. The coil has a magnetic field inducted into it and thus, current flows through the wire and can be measured without invading the circuit.
I'm trying to measure the varying current on a DC line (5A max @ 15v *ish) without paying too much for an expensive hall effect sensor, or putting a high rated resistor in series. My circuit should only be worried when I'm approaching the max current and I'll probably use a potential divider and a comparator to detect this.
So my idea is; would applying a square trace right next to the current line on a PCB like an antenna, induct any current, and would it be measurable? Could I bypass buying expensive components and tune a comparator to detect the inductance myself work?