This paper deals with estimating the sensitivity of equal- and unequal-arm laser deformographs of various modifications. Estimates account for measurement errors caused by: (1) stability of laser radiation frequency; (2) temperature, humidity, and pressure variations; and, (3) noise of photoelectric devices. It is shown both theoretically and experimentally that in order to increase the sensitivity of deformographs, their supports should be mounted on media with different characteristics and pendulum systems should be used. Some results of correlated measurements with two laser deformographs spaced 250 km apart are presented.