The collapsible single- and double-blade rotary paddles represent an excellent solution for use inside bins that handle light to medium weight materials such as feeds, seeds and grains or materials where more surface area is needed to apply resistance to the paddle and activate alerts (two-vain), or heavy materials that need minimal contact to activate an alert (single-vane). Their unique collapsible design allows them to fit trough standard 1-1/4 or 1-1/2 couplings, avoiding safety issues and OSHA violations, by removing the need for personnel to climb into the bin to install the device. These paddles automatically open, once they pass the wall and are ready for immediate use. They are installed by screwing the rotary into the coupling or mounting plate and removed by simply pulling them back through the opening.