Gravitationally lensed quasars are mirages where a background quasar is observed several times due to the light deflection by a foreground galaxy. Microlensing along the individual light paths causes variability of the quasar images, which lets us draw conclusions on the microlensing objects and the quasar engine. I sum up the state of the art and describe our monitoring program which uses the LCOGT robotic telescopes.