The aim was to create an alarm for a mobile phone or a mobile terminal (PDA) using ultrasound waves. This alarm can indicate when the mobile is away from the alarm device at a certain distance. This helps prevent loss or theft of the phone as the alarm goes off a few seconds of not receiving the signal transmitted from the mobile.

This signal transmitted by the mobile is through ultrasound waves. To give this signal periodically (every few seconds), the mobile phone or mobile device (PDA) must have a program. This application or program is developed in a language that can be run on the operating system that uses the mobile terminal.

These signals are transmitted by the mobile sound waves and are not audible to humans.
The transmission of these waves by the mobile phone or mobile device (PDA) is performed by the acoustic transducer in that features the phone itself (headset or speaker).

Both the transmitter and the receiver have different channels that allow multiple phones in the same space to use this alarm.