A dishwasher (1) (30) having a box-shaped casing (2) having an inner wash chamber (3) communicating externally through an opening (4) formed in one of the lateral walls of the casing (2); and at least one dish rack basket (6) housed inside the wash chamber (3) to house dishes/cutlery within a hold volume (7) bounded by two predetermined boundary planes (A, B); the dishwasher (1) having an alarm device (9) which generates, inside the wash chamber (3), at least one light beam in a direction coplanar with a reference plane (R) lying in one of the predetermined boundary planes (A, B); and the alarm device (9) alerting the user to incorrect positioning of the dishes/cutlery inside the basket (6) when the light beam is interrupted by the dishes/cutlery.