Airbags are a supplementary restraint system that inflates during a crash to prevent occupants from hitting the vehicle's interior. The three main components are the airbag module, diagnostic unit, and crash sensors. The airbag module contains the airbag and inflator unit. The diagnostic unit monitors readiness and the sensors detect crashes over 8 mph to trigger deployment. Advanced smart restraint systems adapt deployment based on crash details and occupants detected through various sensors.