A device for therapeutic treatment of a target, in particular an organ or tissue, wherein the device comprises: - at least one ultrasound transducer, in particular a HIFU transducer, for generating and transmitting ultrasound pulses with a frequency (f) to said target, - at least one detector adapted to detect ultrasound waves backscattered from structures between said at least one transducer and said target, in particular a skin, - a signal processing unit adapted to select a first frequency range of an output of the at least one detector caused by backscattered waves having a frequency within a frequency band around an even harmonics of said emitted frequency (f) of said ultrasound pulses, preferably around the second harmonics, - a processor adapted to provide a first output indicative of a parameter of the backscattered waves in said frequency band around the even harmonics, said parameter being an energy of the backscattered waves in said band around the even harmonics, wherein the processor is further adapted to calculate if the parameter of the backscattered waves in the frequency band is above a threshold and wherein the processor is adapted to provide an alert signal in case said parameter is above said threshold, - the frequency band around the even harmonics is based on at least one of the filters, the sampling rate of the signal, the HIFU frequency (f) and the processed signal refresh rate and preferably is 100kHz to 1 kHz, more preferably +/- 25 kHz around the frequency of the even harmonic, characterized in that the signal processing unit is further adapted to select a second frequency range of the output of the at least one detector caused by the backscattered waves, the second frequency range being in subharmonic ranges lower than said emitted frequency (f) of said ultrasound pulses and/or neighboring but not including the even harmonics, wherein the processor is further adapted to provide a second output indicative of a parameter of the backscattered waves in said second frequency range, and wherein the processor is adapted to monitor said first and second outputs in parallel. - at least one ultrasound transducer, in particular a HIFU transducer, for generating and transmitting ultrasound pulses with a frequency (f) to said target, - at least one detector adapted to detect ultrasound waves backscattered from structures between said at least one transducer and said target, in particular a skin, - a signal processing unit adapted to select a first frequency range of an output of the at least one detector caused by backscattered waves having a frequency within a frequency band around an even harmonics of said emitted frequency (f) of said ultrasound pulses, preferably around the second harmonics, - a processor adapted to provide a first output indicative of a parameter of the backscattered waves in said frequency band around the even harmonics, said parameter being an energy of the backscattered waves in said band around the even harmonics, wherein the processor is further adapted to calculate if the parameter of the backscattered waves in the frequency band is above a threshold and wherein the processor is adapted to provide an alert signal in case said parameter is above said threshold, - the frequency band around the even harmonics is based on at least one of the filters, the sampling rate of the signal, the HIFU frequency (f) and the processed signal refresh rate and preferably is 100kHz to 1 kHz, more preferably +/- 25 kHz around the frequency of the even harmonic, characterized in that the signal processing unit is further adapted to select a second frequency range of the output of the at least one detector caused by the backscattered waves, the second frequency range being in subharmonic ranges lower than said emitted frequency (f) of said ultrasound pulses and/or neighboring but not including the even harmonics, wherein the processor is further adapted to provide a second output indicative of a parameter of the backscattered waves in said second frequency range, and wherein the processor is adapted to monitor said first and second outputs in parallel. the signal processing unit is further adapted to select a second frequency range of the output of the at least one detector caused by the backscattered waves, the second frequency range being in subharmonic ranges lower than said emitted frequency (f) of said ultrasound pulses and/or neighboring but not including the even harmonics, wherein the processor is further adapted to provide a second output indicative of a parameter of the backscattered waves in said second frequency range, and wherein the processor is adapted to monitor said first and second outputs in parallel.