Interior monitoring system of a vehicle wherein at least one transducer is arranged on a first side of the structure of the vehicle and transmits waves toward an opposite, second side of the structure so that any objects contained in the interior space of the structure are situated between the first and second sides. Each transducer receives waves reflected from any objects between the first and second sides. A processor is coupled to each transducer and obtains information about any objects from which waves have been reflected and received thereby. Each transducer may be arranged to transmit infrared waves into the interior space, e.g., infrared waves in an eye-safe range.