A link arm for securing bicycles and other vehicles and their components to each other and to fixed objects such as bike racks and street poles. The link arm is composed of a plurality of elements flexibly joined to each other by cylindrical joints, joined to the bicycle or vehicle by a perpendicularly oriented central hinge, allowing for restricted movement and rotation of other elements in the link arm. The link arm is designed to, when fastened, form a closed loop around the bicycle or vehicle frame, wheel and bike rack. When not in use, the device can be folded into a neat, compact configuration for convenient storage. The central perpendicular hinge enables fast and simple transition between the two states of fastened and in storage.