Highly sensitive pyroelectric IR sensors were fabricated with La-modified $PbTiO_{3}(PLT)$ thin plates compensating for piezoelectric effect. The device was fabricated in a dual form by placing two PLT cells, each of $1{ imes}2;mm^{2}$, side by side with appropriate electrode configuration. The dual element sensor had a signal to noise ratio of about 350 that was much larger than that of single element sensors. Further the dual element sensors exhibited excellent pyroelectric properties such as a large voltage responsivity of 2400 V/W, a pyro-coefficient of $4.6{ imes}10^{-8};C/cm^{2}K$, a voltage figure of merit of $4.2{ imes}10^{-11};Ccm/J$, and a small thermal time constant of 8.7 msec. It was confirmed through experiments that the dual element sensor was applicable to detect the two-dimensional moving direction of human beings.