This is the most secure mounting option. It will leave two small holes on the dash once the unit is removed. Use the included self-tapping screws to mount the unit (rectangular side with hooks) in the desired position in your vehicle where you want the ignition interlock to sit. A standard Philips screw driver will suffice, and the screws can be inserted anywhere on the back of the unit near the hooks.
The unit also includes a Velcro adhesive option. Dash boards are made to be stain and stick proof, and mounting the holster using adhesive is not as effective as using screws. It will minimize any lasting marks on the dash.