Nuki has introduced the fifth generation of its Smart Locks, maintaining the brand’s signature illuminated ring while compressing the mechanics into a markedly smaller footprint. Roughly a decade after presenting its prototype on a crowdfunding platform, the company from Graz reports more than a million users and over 400,000 active electronic locks worldwide. The latest Smart Lock Pro and Smart Lock Ultra feature a compact design with fully reworked mechanics. In this redesign, Plexiglas molding compounds from Röhm were selected for light-guiding components to deliver the intended visual signaling without expanding the device’s dimensions.
The illuminated ring has been a trademark of Nuki since the first product generation. The design objective was to create an intuitive, unambiguous indication of lock status. “The question that guided us was: How can we show intuitively whether the lock is locked or unlocked?” said Alexander Ketter, Head of Operations at Nuki Home Solutions GmbH, recalling the collaboration with Vienna-based design studio EOOS. He added that the team deliberately avoided a padlock icon and traffic-light colors. According to Ketter, red and green could be interpreted differently depending on intent, and are problematic for users with color vision deficiencies. The solution was a segmented light circle, with a full circle indicating locked and a three-quarter circle indicating unlocked.
The light ring is the signature design feature of Smart Locks from Nuki. When unlocked, the top segment of the illuminated ring remains unlit. Plexiglas Softlight guarantees homogeneous light scattering.
Addressing market acceptance and installation constraints, the new Smart Lock Pro and Smart Lock Ultra have been reduced to roughly a third of their original size. “The smaller a retrofit electronic door lock is and the more subtly it fits into the existing system, the greater the acceptance among customers. However, miniaturization also makes the design much more complex and limits the technical possibilities,” explained Ketter. The redesign was executed by XITEC Engineering GmbH, which consolidated both mechanics and drive into the rotating cylinder, removing the previous box-shaped substructure. “The inside of the Nuki Smart Lock contains around 60 components developed in house, not one of them is a standard part,” said Andreas Rainer, graduate engineer and Technical Lead at XITEC. The new models employ a brushless motor for rapid, efficient operation and a more compact layout.
Light guidance integrated with compact mechanics
“Light guidance and light scattering were major challenges in the redesign. After all, Nuki was clear that the signature light circle had to stay,” said Rainer. During locking and unlocking, the cylinder rotates, yet the open segment of the ring had to remain at the top from the user’s perspective. Achieving this visual effect in tight space required deflecting LED light by 90 degrees. A combined design approach and two Plexiglas grades with distinct properties were used to reconcile optical and mechanical requirements. “For this complex design, Nuki needed both a light-scattering Plexiglas molding compound to allow homogeneous illumination of the ring, and a transparent Plexiglas version with very high mechanical stability, so that the light-guiding components can withstand the torque of the tooth flanks,” said Christian Bitsch, Senior Market Tech Consulting Manager in the Molding Compounds business unit at Röhm.
Diffuser-based homogenization using Plexiglas Softlight
The ring illumination is generated by a diffuser placed over a circuit board carrying eight LEDs arranged in a circle. The diffuser is manufactured from light-scattering Plexiglas Softlight, with a white plastic reflector, in a two-component injection molding process. Plexiglas Softlight transforms the LEDs’ point sources into a soft, uniform output and supports controlled deflection due to diffuser particles in the material. “The diffuser molding compound offers enormous freedom of design for all kinds of lighting applications, such as ambient lighting. The variants in the product family are available with different densities of diffuser particles for forward and backward light scattering,” Bitsch specified.
Smart Lock from Nuki: The full circle light ring shows that the door is locked. Two components made from Plexiglas molding compounds from Röhm enable this light effect in the fifth product generation.
Mechanical light guide with Plexiglas Resist
A separate hybrid component made from transparent Plexiglas Resist with a metal insert couples the mechanical motion with the optical signaling. The selected molding compound is impact modified while retaining high-quality light-guiding behavior. “This component rotates with the drive unit and has to withstand enormous mechanical stress. It is designed for a torque of up to 5 Newton meters,” Rainer noted. The light guide is disk-shaped, with a thin crown in the center that engages the ring-shaped opening of the rotating cylinder. At this interface, the light diffused by Plexiglas Softlight becomes visible to users as the slender illuminated ring.
he Nuki Smart Lock Pro and the smaller Nuki Smart Lock Ultra feature a light guide that works together with the rotating mechanics and is visible only as a slim light ring from the outside. Two components made from Plexiglas molding compounds make the li
The development program lasted four years. The Nuki Smart Lock Ultra was named CES Innovation Awards Honoree 2025 in the Smart Home category at the CES technology trade fair in Las Vegas, recognizing its design and technical integration of mechanics and optics in a condensed form factor.
