Abstract: The invention concerns a window including at least a first sheet (16), a second sheet (18), said sheets being joined together by a connecting layer (20), characterised in that it also includes an ultrasonic device (12) placed between said sheets (16,18) and co-operating directly with a first face (24) of said first sheet (16) to detect the presence of foreign bodies on a second face (26) of said first sheet (16) opposite said first face (24), said device (12) comprising a transducer (28) able to emit, via a transmitting/receiving face, an incidental ultrasonic signal of wavelength .lambda. in said first sheet (16), the thickness of said first sheet being equal to K..lambda./2, where K is an integral number, and said transducer being able to receive, via said transmitting/receiving face a reflected ultrasonic signal representative of the presence or absence of said foreign bodies to generate a detection signal.