The SIEMENS QBM81-5 is a precision differential pressure switch designed for accurate monitoring and control of low-pressure air systems in HVAC and industrial environments. It features a potential-free digital output (CO: 1) supporting switching voltages of AC 24–250 V or 24 V DC, with a switching current range of 0.01–5 (3) A, ensuring reliable signal transmission and control flexibility. The device operates at permissible pressures up to 7.5 kPa and offers a measurement range of 50–500 Pa, making it suitable for airflow and filter monitoring applications. Engineered for durability, it operates within an ambient temperature range of -20 to +85 °C and provides IP54 protection against dust and moisture. Designed for vertical diaphragm mounting with the pressure connection facing downward, the QBM81-5 includes a 6.2 mm connection branch and compact dimensions of 81 × 90 mm. The SIEMENS QBM81-5 may be utilized in North America, Europe, Asia, and worldwide installations requiring robust, high-accuracy differential pressure monitoring in ventilation and control systems.