Siemens FDA241 aspirating smoke detector utilizes two sensing wavelengths to differentiate between smoke and deceptive phenomena, enabling increased detection reliability even in challenging environments. It can detect smoldering or off-gas particles up to five times earlier than competitive spot detectors, decreasing the risk of thermal runaway in a lithium-ion battery energy storage system. The patented dual-wavelength technology uses blue and red wavelengths to detect small off-gas particles that are produced in the early stages of battery failure and overheating. Using two wavelengths allows the detector to differentiate dust and steam particles from smoke and off-gas particles, thus signaling the appropriate warning signal and minimizing potential false alarms. The FDA241 has a VdS approval (no. S 619002) and performance verification as an early warning detection device for lithium-ion battery off-gas detection. This VdS approval can be used to meet NFPA 855 requirements through equivalency allowance in NFPA 72 section 1.5.