The present disclosure provides an alert device and an alert method. The alert device includes an image capturing unit, an input/output unit and a processing unit. The image capturing unit is configured to capture at least one image of a wafer transportation system. The processing unit is configured to: retrieve the at least one image from the image capturing unit; define a first boundary in the at least one image; identify a wafer chuck of the wafer transportation system in the at least one image; determine whether the wafer chuck intersects the first boundary in the at least one image; and transmit an alert signal to the wafer transportation system via the input/output unit when the wafer chuck is determined to intersect the first boundary in the at least one image.