35 is applied over the exterior surface of wall 25 and thermally insulated therefrom in order to respond to pressure on or heat directed toward the exterior surface of the cabinet the adhesive layers 40 and 43 are like the layer 40 in fig9 the overcoat 45 is preferably transparent to infrared radiation to enable the transducer 35 to respond to the body heat of an individual in close proximity to the cabinet the manner in which transducer 36 is applied to cabinet door 26 is similar to that in which transducer 35 is applied to wall 26 in fig1 a block diagram of signal processor 50 is shown in fig1 the two leads from each of the transducers 31 36 are connected to a corresponding high input impedance amplifier 51a 51f respectively the amplifiers 51a 51f are preferably placed close to the transducers to keep each transducer 39 s leads 14 and 15 short this helps to minimize noise pick up in those leads the output of each of the amplifiers 51 is connected to the input of a corresponding adaptive filter system 60a 60f these adaptive filter systems improve the signal to noise ratios of the transducer output signals of interest by subtracting background noise adaptive filter system 60a is shown in block diagram form in fig1 and is discussed more fully.