In one embodiment, a mobile device (e.g., a smartphone) is utilized to determine whether a user has paid for parking. The mobile device collects sensor data that describes actions of a mobile device or actions of an automobile or of a driver of the automobile. The sensor data includes one or more of location data, acceleration data, rotational data, or audio data. Either the mobile device or a centralized server performs an analysis of the sensor data to determine data indicative of a pay status of the parking spot. The pay status indicates whether the user has likely paid for parking. The mobile device or the centralized server is configured to generate a message based on the data indicative of the pay status of the parking spot.