Safety-critical electronic control units within automotive applications, such as four-wheel-drive, anti-lock braking systems, and airbag systems, are all characterized by sophisticated internal and external monitoring circuitry. This paper is focused on the specific needs of monitoring circuitry in electronic control units (ECU) for airbag systems.After a short introduction, the main electrical components of an airbag system and their interconnections are described. In the following sections, the monitoring of components external to the ECU is discussed, such as the monitoring of the battery supply voltage, the warning lamp, the selection inputs, the firing loops, and external crash sensors. For each case, requirements are stated and practical solutions for the realization of the monitoring functions are provided. Furthermore, the pros and cons of simple and sophisticated solutions are compared.