Currently, the number of various crimes such as robbery of articles placed inside cars and illegal entry of another's residence has been increasing, and the consciousness of people for crime prevention has been growing. To meet the demand generated with the increase in consciousness for crime prevention, a variety of crime-prevention goods have been developed.
For example, a security mechanism control system which locks and unlocks doors of a vehicle has been developed as an example of a security mechanism control system for a vehicle using radio waves. For example, according to security mechanism control systems disclosed in Patent Reference No. 1 (JP-A-2003-27790, publication date: Jan. 29, 2003), Patent Reference No. 2 (JP-A-2003-27791, publication date: Jan. 29, 2003), and Patent Reference No. 3 (JP-A-2003-301638, publication date: Oct. 24, 2003) or other references, a user can automatically lock or unlock a vehicle only by carrying a portable device and easily check that the vehicle has been locked. In these security mechanism control systems, the portable device transmits signals and a main device receives the signals. Thus, the user carrying the portable device can automatically unlock the vehicle only by approaching the vehicle and lock the vehicle by moving away from the vehicle.
In such a conventional type of security mechanism control system which automatically locks and unlocks doors of a vehicle when the user carrying the portable device gets into and out of the vehicle, a plurality of portable devices are prepared and separately used in some cases when the security target such as a vehicle is used by a plurality of users.
When the plural portable devices are used, however, the possibility that any of the portable devices is left inside the vehicle increases. If any of the plural portable devices is left inside the vehicle, the following problem occurs according to the conventional system.
Since the left portable device is located inside the vehicle, the main device determines that the user as the owner of the portable device is still staying inside the vehicle and does not automatically set the security condition for the vehicle in some cases. When this occurs, the user does not notice that the portable device has been left inside the vehicle and leaves the vehicle in the non-security condition.
In another case, each of the plural users has his/her portable device and the security mechanism control system automatically locks the vehicle when any of the plural users gets off the vehicle. In still another case, the user locks the vehicle by directly giving a locking command to the vehicle.
In either of these cases, the vehicle is automatically unlocked by the approach of a person other than the users when any of the portable devices is left inside the vehicle. This is because the requirements that a person is approaching the vehicle and that the portable device is positioned near the main device are satisfied, and therefore the locking condition set for the vehicle is automatically cancelled.
Moreover, when the plural portable devices are used in the system, such a case can happen where a user carrying the portable device moves away from the main device but another user stays near the main body.
In this case, the user leaving the vehicle considers that the vehicle has been automatically locked, but in reality the vehicle is not locked since the other user stays near the main device. Thus, the operation of the system depends on the behaviors of the users. There is a possibility that the requirement for unlocking is satisfied while the requirement for locking is satisfied. The above case is a result of the operation selected by the main body which has determined that the vehicle should be unlocked.
Therefore, when the plural portable devices are used, the main device does not always set the condition as the user desires.
According to the structures shown in Patent Reference Nos. 1 through 3, when the portable device left near the main body or carried by the user is positioned near the main body, the problems mentioned above cannot be solved. This is because the system does not have means for determining whether the portable device near the main body is the device left behind or the portable device carried by the user, nor means for appropriately notifying the user of the result of the determination.
In the structures shown in Patent Reference Nos. 1 through 3, therefore, in case of the plural portable devices are used, the vehicle cannot be locked or the locked condition is cancelled against the user's intension while the user is not noticing this situation.