Very good idea. Clever software desirable.

Quite funny part. Once you move away (I suppose once the Bluetooth connection is lost) suggests the sensor and the smartphone alarm. In the smartphone you can (with the associated software from the store) then display on a map, where most recently a GPS location was saved.

However, the thing is sometimes overzealous and reports a signal for no apparent reason. Full practicable, it is then not for every conceivable application.

Nevertheless, 4 points, good for the idea and the basic functioning. Perhaps the manufacturer can offer even more settings for the user. About a time delay for triggering the warning signal.