Double Cylinder Function: Schlage double cylinder handlesets require a key to unlock the mechanism on both the interior and exterior sides of the door. Double cylinder locks can pose a safety hazard in times of emergency due to requiring a key to unlock from the inside; please check local codes before installing. The timeless design of the Plymouth works with any style in any room of your home. Note: New interior packs will not work with old exterior packs. New exterior handlesets will not work with old interior packs. Model Conversions: