The FLAG DELIVERY SENSOR is an indicator that comprises an elongated rod forming a flag staff with one of its ends connected to a coiled spring attached by a bracket to the right side of the mailbox. These Sensors operate on the principle that an object interrupts or reflects light, so they are not limited like Proximity Sensors to detecting metal objects. This means they can be used to detect virtually any object, including glass, plastic, wood, and liquid. The FLAG
DELIVERY SENSOR is very effective and useful.