An ultrasound device for therapeutic and aesthetic treatment is disclosed. Different types of hand probes used with the device produce different effects within biological tissues. The device can operate at low frequencies of around 20 KHz to 100 KHz. The device can be operated in continuous mode or pulsed mode with different duty cycles. Software and hardware is used to control power output of the hand probes; treatment time; to perform diagnostics of the hand probes; and to shut off ultrasound emissions in the case of abnormal or incorrect functioning of the hand probes.