I've never done anything with hall effect sensors. I don't understand them. What do they do?
They sense magnetic fields. When current moves through a conductor (like wire) it makes a field. Alternating current makes the field change directions.
Hall sensors have an axis to them so you might have to get that aligned. They also come in different packages; some are purely on/off and some you can get analog readings through.
In the US the AC is 60 cycles per second and used to drive clocks since before even transistors. It's also just right to upset heart signals which is why a plugged in radio dropped in the tub is usually lethal.
In Europe the AC is 50 cycle which I have read does not fibrillate hearts.
Note: your power line may be 'dirty'/have spikes but those can be coded for. X10 control systems will also add small waves to the power line, those are the things that use house power as control lines for various devices.