A system detects the presence of a living being within a vehicle and triggers an alarm should the temperature rise above or fall below a predetermined threshold limit. The system uses a carbon dioxide monitor to determine for the living being's presence, which is backed up by one or more subsystems that include a motion sensor that senses motion, a sound sensor that senses sounds, especially those made by distressed living beings, and a camera that uses facial recognition software to detect a face within the vehicle. The alarm can be staged so that a lower level of alarm is triggered when the hazardous temperature is approaching, but has not yet reached critical levels, and one of the subsystems has detected a living being within the vehicle, but the others have not yet activated, and a higher level alarm once critical temperatures have been reached.