Lasers can be identified by their relatively long coherence lengths using interferometry. A Mach–Zehnder interferometer incorporating liquid crystal polarization modulators is demonstrated as a means of low-cost, robust laser detection. Temporal modulations, as a signature of coherence, can be induced by modulating polarization changes in liquid crystal modulators using low voltages. Sensitivities of <10  nW can be achieved. The suitability as a means of laser detection is discussed.