PLEXIGLAS® molding compounds enable smart light solution in new Nuki Smart Locks

• Nuki Home Solutions launches new compact generation of keyless locks with innovative mechatronics
• Light-scattering PLEXIGLAS® Softlight allows segmented, homogeneous illumination of characteristic light ring
• Impact-resistant PLEXIGLAS® Resist enables mechanics and light signals to work together

The unmistakable mark of a Smart Lock by Nuki is an illuminated ring that signals whether a door is locked or unlocked. Around ten years after the prototype was showcased on a crowdfunding platform, the company from Graz, Austria, is now one of the European market leaders in electronic access solutions. More than a million people worldwide use Nuki’s smart access solution, with more than 400,000 active electronic locks. These locks not only enable keyless access to private homes and vacation rentals, but also remote access control using an app.

Now Nuki has launched the fifth product generation, featuring a compact design and fully revamped mechanics. In this complex redesign, PLEXIGLAS® molding compounds from Röhm were part of the solution.

Nuki’s trademark light ring

The light ring is a perfect example of successful communication design using light, and has been Nuki’s trademark since day one. “The question that guided us was: How can we show intuitively whether the lock is locked or unlocked?” says Alexander Ketter, Head of Operations at Nuki Home Solutions GmbH, describing how the idea was formed in collaboration with Vienna-based design studio EOOS. “We did not want to use the ubiquitous padlock symbol, nor red and green light signals.” Red and green could be interpreted differently depending on the user’s intention, he argues, with green signaling either a securely locked door or open access. Furthermore, people with color blindness will have a hard time distinguishing between the colors.

The design team ultimately opted for the segmented light circle as a clear signal: a full circle for “locked” and a three-quarter circle for “unlocked.”

The challenge of miniaturization

The new Smart Lock Pro and Smart Lock Ultra models have been reduced to 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,” explains Ketter.

The complex redesign was undertaken by engineers at XITEC Engineering GmbH, a development office for mechatronic components and products. The rotating cylinder now houses both the mechanics and the drive, eliminating the need for the box-shaped substructure in the previous model. This involved downsizing and re-engineering all components from the ground up using innovative technology and different materials, including PLEXIGLAS® for the light-guiding components.

“The inside of the Nuki Smart Lock contains around 60 components developed in house – not one of them is a standard part,” says Andreas Rainer, graduate engineer and Technical Lead at XITEC. The Smart Lock Pro and Smart Lock Ultra are equipped with a brushless motor that works rapidly and efficiently, while also enabling a more compact design.

Linking mechanics and light guides

“Light guidance and light scattering were major challenges in the redesign. After all, Nuki was clear that the signature light circle had to stay,” says Rainer. The Smart Lock cylinder turns during locking and unlocking, but the light circle was to look as though it did not. The open segment was to remain in the same position at the top. To achieve this in the new design with limited space, the LED light needed to be deflected by 90°. A clever design trick and two PLEXIGLAS® products with different properties made a smart solution possible.

“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,” says Christian Bitsch, Senior Market Tech Consulting Manager in the Molding Compounds business unit at Röhm.

PLEXIGLAS® Softlight illuminates the light ring homogeneously

A diffuser over the circuit board with eight LEDs arranged in a circle creates the light diffusion. It is produced from light-scattering PLEXIGLAS® Softlight and a white plastic as a reflector in a two-component injection molding process. PLEXIGLAS® Softlight transforms the intense point lighting of the LEDs into a soft, homogeneous light and deflects it thanks to the diffuser particles contained 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,” specifies Bitsch.

Component with PLEXIGLAS® Resist acts as mechanical light guide

A separate hybrid component made from transparent PLEXIGLAS® Resist with a metal insert allows the mechanics and the light signal to work together. The special molding compound used for this has been modified to be impact resistant while also offering excellent light-guiding properties. “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,” explains XITEC engineer Rainer.

The light guide made from PLEXIGLAS® Resist is shaped like a disk, with a thin crown in the center. The crown is inserted into the ring-shaped opening of the rotating cylinder. This is the point at which the light that has already been scattered by PLEXIGLAS® Softlight becomes visible to end users as an illuminated ring.

The four years of development have already paid off, as the new 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 for its innovative design and technical properties.