To provide a car security device capable of properly outputting an alarm according to a time zone.

This car security device is provided with a detection means 10 for detecting a state change of a vehicle, an alarm output means 13 capable of outputting an alarm, an abnormality decision means 12 for deciding the presence or absence of occurrence of an abnormality based on a sensor output of the detection means 10, an alarm output means 13 for outputting the alarm when the occurrence of the abnormality is decided by the abnormality decision means 12, an illuminance sensor 15 for detecting brightness, and a time zone estimation means 16 for estimating the present time zone based on an output of the illuminance sensor 15. A mode of the alarm output is changed according to the time zone estimated by the time zone estimation means 16.