The Heusser inset lock Series 9 is a fitting system for emergency doors, whose 3 shells and 2 handles can be combined to create solutions for a range of applications. The most innovative product in the series is the S9.42.D3 inset lock, which combines flush-mounting, compliance with the DIN EN 179 standard, and a low installation depth. As part of a flush-mounted application, the two-level design reduces the required door thickness by up to 20 mm. The high-quality, compliant form targets an extension of the range of applications into demanding architectural contexts.