current sensors

[bambam01]

Hello im just getting into electronics and know very little as yet im trying to understand current sensors and how they work.

Does a current sensor that senses ac current that is part of a dc circuit work like a switch that is normally open or normally closed when current pass through them?

Or do they generate an electronic signal that triggers something else within the dc circuit when current ether passes in or out of its parameters?

if they do work in this way is it possible to have a current sensor transmit a signal when current stops passing through its parameters as to trigger something like a switch or can they only do this when current passes through its triggering point?

Would it be difficult to add something to adjust the sensitivity of a current sensor like the control on a thermostat?