Abstract: A double feed detector to detect the feeding of multiple sheets into processing equipment such as printing presses which includes a reciprocally mounted gauge tube with a passage opening onto its opposite ends so that one of its ends is lowered into a gauging position over a support surface on which the sheets being fed are located. A pressurized air supply is connected to the gauge tube intermediate its ends and a cap closes that end of the passage opposite the end at the support surface so that, when more than one sheet is located on the support surface, the rise in air pressure in the gauge tube will urge the cap against a switch to stop the sheet feed to the processing equipment.