A restraining device that can be positioned and secured using one hand includes a housing, a strap, a handle, and a locking unit. The housing has a pair of apertures positioned singly in front and rear ends thereof. The strap, which has a first end engaged to the housing, extends from the housing loopedly back through the pair of apertures to define a loop. A second end of the strap is external to the housing. The handle is engaged to the strap proximate to the second end. Hands of a person can be inserted into the loop so that the strap is positioned around wrists of the person. A user is positioned to pull on the handle to tighten the strap around the wrists. The locking unit, which is engaged to and positioned in the housing, can selectively engage the strap to prevent expansion of the loop.