A detector, system and method for detecting vehicle lock status are provided. The detector comprises a motion sensor configured to sense vehicle door open and close movement; a microphone configured to record sound patterns generated with targeted events; a wireless communication module; a memory for storage; a battery for supplying power; and a controller connected to the motion sensor, microphone, wireless communication module, memory and battery respectively and configured to switch on or off the microphone and the wireless communication module according to signals provided by the motion sensor, and control the wireless communication module to transmit sound files wirelessly. The detector is designed and sized to be attached to the vehicle door. The detector is easy to use, easy to install, yet affordable for detecting the lock status of the vehicle and show the lock status on the driver's smart phone even if he/she has walked away.