A safety system and a method configured to determine whether a passenger compartment of a vehicle is occupied whether the temperature of the passenger compartment is outside an acceptable temperature range, and to take a safety countermeasure if needed. An occupant is detected by sounds received by an audio transducer within the passenger compartment connected to an infotainment system. The temperature is detected by a temperature sensor connected to the heating, ventilation and air condition system of the vehicle. Example safety countermeasures include activating the horn, transmitting a wireless signal indicating that an unattended occupant is in the vehicle to a remote wireless receiver, and/or at least partially opening a vehicle window. A pair of high frequency speakers connected to the infotainment system may be used to transmit and receive ultrasonic signals so that an occupant may be detected using ultrasonic motion detection techniques.