This application relates to the field of intelligent hardware, and in particular, to an intelligent scenario in which a mobile terminal and a car are combined. After detecting, by using an acceleration sensor and a gyroscope of the mobile terminal, that a car engine stops, the mobile terminal receives, from a sensor installed near a roof lamp of the car, a signal indicating that the roof lamp is on, and determines that a door of the car is opened. In this case, the mobile terminal sends a reminder to a user.