2012 Toyota Prius Owners Manual - Page 356

1-2. Key information Using the mechanical key (vehicles with a smart key system) To take out the mechanical key, slide the release lever and take the key out. The mechanical key can only be inserted in one direction, as the key only has grooves on one side. If the key cannot be inserted in a lock cylinder, turn it over and re-attempt to insert it. After using the mechanical key, store it in the electronic key. Carry the mechanical key together with the electronic key. If the electronic key battery is depleted or the entry function does not operate properly, you will need the mechanical key. (→P. 473)