  We present here how a coherent perfect absorber-laser (CPAL) enabled by
parity-time ($\mathcal{PT}$)-symmetry breaking may be exploited to build
monochromatic amplifying devices for flexural waves. The fourth order partial
differential equation governing the propagation of flexural waves leads to four
by four transfer matrices, and this results in physical properties of the
$\mathcal{PT}$-symmetry specific to elastic plate systems. We thus demonstrate
the possibility of using CPAL for such systems and we argue the possibility of
using this concept to detect extremely small-scale vibration perturbations with
important outcomes in surface science (imaging of nanometer vibration) and
geophysics (improving seismic sensors like velocimeters). The device can also
generate finite signals using very low exciting intensities. The system can
alternatively be used as a perfect absorber for flexural energy by tailoring
the left and right incident wave for energy harvesting applications.
