A sensor bar shelf monitor, for example that may be added to an existing shelving system to convert a store to autonomous operation. The sensor bar may contain distance sensor to detect shoppers reaching towards items on a shelf, and cameras to determine which items shoppers have taken. It may be installed into shelf supports such as gondola shelving uprights. The sensor bar may be located at the front edge of a shelf, and may monitor the shelf below. Placing the sensor bar along the front edge prevents damage to electronics from spills or shelf cleaning, and prevents heat from the sensor bar electronics from damaging items on the shelf. The sensor bar may have a local sensor bar processor that collects sensor data; images may be analyzed locally or transferred to more powerful store processors. A sensor bar may also have controllable lights and controllable electronic labels.