Apart from current sense monitoring using a resistor, like  Microhm current sense resistor MMS Series, two other less common methods are used. One uses a Hall Effect sensor to measure the flux field generated by a current. While this is non-intrusive and has the advantage of no insertion loss, it is somewhat expensive and requires a relatively large amount of PCB real estate. The other method, using a transformer to measure induced AC current, is also size and cost intensive; while also useful only for AC current.

 
If using a resistor, we need to pay attention to the three basic aspects as below:
 
Choosing a low resistance precision sense resistor. If real estate is based on location, then choosing a resistor is based on precision.
 
Choosing a sense amplifier chip. When sensing voltages across a resistance that is less than one ohm, small changes in voltage can have significant sense consequences. The sense amplifier amplifies that voltage change, making the insignificant, significant.
 
The location of the sense resistor. This refers to either sensing at the power supply, called High-Side Sensing, or at the ground connection, called Low-Side Sensing.
 
Precision current sensing applications are no longer made-from-scratch circuits; manufacturers have done all of the research and most of the work for modern designers.

 
Current sense monitoring helps to improve the efficiency of some systems and reduce losses. For example, many mobile phones have implemented current sensing to monitor and improve battery life while also improving reliability. If the current draw becomes too large, the phone can decide to throttle back the CPU frequency to reduce the load on the battery in order to extend battery life, while preventing the phone from overheating which increases reliability. There are even phone apps that can access the current sense reading circuit and make decisions to optimize the phone’s performance. Microhm current sense resistors with tight size, high precision, low ohm are especially fix for this kind of applications.