Abstract: A vehicle presence detecting sensor (10) associated with a defined area, wherein, the sensor (10) comprises a microprocessor (100), and a first detecting module (11), a second detecting module (12), as well as a third module (13), respectively connected to and controlled by the microprocessor (100), wherein, the microprocessor (100) is configured for activating the second detecting module (12) when a change of magnetic field is detected by the first detecting module (11) or activating the third module (13) when the distance measured falls out of the predetermined distance range, and for confirming the presence of a vehicle by comparing the distance measured by the second detecting module (12) with a predetermined distance range, or by matching the value of the detailed change of magnetic field detected by the third module (13), with prestored values. Also, a method of the sensor (10) and a self enforcing pay-by-phone parking system using the sensor (10) are disclosed.