A unique aspect of safety electronics for auto-mobiles is the need for redundancy in design and for exten- sive monitoring, both internal and external, of embedded circuitry. Supplemental restraint systems (SRSs), which control airbags and sometimes seatbelt pre-tensioners, are an increasingly popular feature in cars. The SRS electronic control module (ECM) controls the deploy- ment of airbags (and often seatbelt pre-tensioners) based on the input of electro-mechanical sensors.