I cannot directly determine the generation of the Nest Protect sensor with the product code S3003LWFD. However, to identify whether a Nest Protect is first or second generation, you can check the physical characteristics such as the rounded edges for the second generation, or look at the serial number on the back label for codes starting with 06A or 06C for the second generation.You can also check the serial number on the back label for codes starting with 06A or 06C for the second generation.