A phase detector or phase comparator is a frequency mixer, analog multiplier, or logic circuit that generates a signal which represents the difference in phase between two signal inputs.

Phasing sticks are specialised test instruments that allow technicians to determine if two electrical conductors are in-phase with each other, measure phase-to-phase voltage, compare phase-to-phase voltage, or test between phase and earth connections.

These devices are generally large in construction but lightweight enough to be moved between a variety of test points during a technician's day. Phasing sticks usually form part of a larger test kit comprising digital voltage indicators and phasing rods with detachable earth lead. The digital voltage indicator can be used by technicians separately from the phasing rod as a voltage stick or voltmeter.