This currently creates an increasingly high pitched tone using a piezo element.

gistfile1.ino

/*
  playMelody
  Appropriated from Tom Igoe's example here:  
  from http://arduinno.cc/en/Tutorial/Tone
 
  Update by Gareth Foote for Arduino Projects and Workshop.
  
  @description
  This currently creates an increasingly high pitched tone
  using a piezo element.
  
  @wiring
  Plug the black wire of the piezo to ground and the red to 
  your selected output pin (see 'int soundOutputPin' variable below)
  
  Note:The other thing to remember is that Piezos have polarity, 
  commercial devices are usually having a red and a black wires 
  indicating how to plug it to the board. ###We connect the black
  one to ground and the red one to the output.###
  ref: http://www.arduino.cc/en/Tutorial/PlayMelody
 
 */
 
 
// You will need to include this line. It is a file that will
// need to be in the same directory as your sketch (.pde). 
// It is a list of pitch frequencies. 
 #include "pitches.h"

// You specify the output pin here which for some reason ISN'T 
// a PWM (analog out).  
int soundOutputPin = 8;

// These are approximate values for the min and max values you
// expect to get back from the bio sensor.
int inputmin = 400;
int inputmax = 1000;

// I am using this variable below in loop() to fake the sensor 
// input you will be getting from the bio sensor. 
int bioSensorInput = 0;

// These are min and max values for the tone that will be playing.
// If it starts too low pitched then increase tonemin and if it
// gets too high pitched then decrease the tonemax. These default
// values are taken from the  file "pitches.h".
int tonemin = 31;
int tonemax = 4978;


// For fun. Ignore
boolean playingDitty = false;

void setup() {
  
  // begin debugging 
  Serial.begin(9600);
  
  // Start from approximate input min value.
  bioSensorInput = inputmin;
  
  // Uncomment the line below for a little ditty. (Just for fun - 
  // please ignore if you need to get real work done!) ;) 
  playLittleDitty();
}

void loop() {
  
   if(playingDitty == true)
   {
     return;
   }
    
   // Incrementing this counter to fake an increasing amount of 
   // conductivity coming from the bio sensors. 
   bioSensorInput++;
   
   // From seeing your prototype in action I estimated that a 
   // max and min of about 400 -> 1000 coming from your input 
   // bio sensor (these values are set at the top of this sketch).
   // Therefore I am resetting this input back to 400 whenever it 
   // gets to 1000;
   if(bioSensorInput >= inputmax)
   {
      // Reset to 400.
      bioSensorInput = inputmin; 
   }
   
   Serial.println(  bioSensorInput );
   
   // You will call this function within your sketch and pass the value
   // you're getting from the bio sensor inputs. Currently the 
   playTone(bioSensorInput, inputmin, inputmax);
    
}


/*
 * Copy this function into your Sketch.
 */
void playTone( int input, int rangemin, int rangemax ) {
 
   int noteDuration = 1000/4;      
   int freq = map(input, rangemin, rangemax, tonemin, tonemax);
   
   tone(soundOutputPin, freq, noteDuration);
        
   int pauseBetweenNotes = noteDuration *1.30;
   delay(pauseBetweenNotes);
   // stop the tone playing:
   noTone(soundOutputPin);
}


/*
 * This is just for fun! please ignore if you need to get real work done! ;) 
 */
 
void playLittleDitty(){

  playingDitty = true;
  
  // notes in the melody:
int melody[] = {
  NOTE_C4, NOTE_G3,NOTE_G3, NOTE_A3, NOTE_G3,0, NOTE_B3, NOTE_C4};

// note durations: 4 = quarter note, 8 = eighth note, etc.:
int noteDurations[] = {
  4, 8, 8, 4,4,4,4,4 };
  
 // iterate over the notes of the melody:
  for (int thisNote = 0; thisNote < 8; thisNote++) {

    // to calculate the note duration, take one second 
    // divided by the note type.
    //e.g. quarter note = 1000 / 4, eighth note = 1000/8, etc.
    int noteDuration = 1000/noteDurations[thisNote];
    tone(8, melody[thisNote],noteDuration);

    // to distinguish the notes, set a minimum time between them.
    // the note's duration + 30% seems to work well:
    int pauseBetweenNotes = noteDuration * 1.30;
    delay(pauseBetweenNotes);
    // stop the tone playing:
    noTone(8);
  }
  
  playingDitty = false;
  
}

pitches.h

/*************************************************
 * Public Constants
 *************************************************/

#define NOTE_B0  31
#define NOTE_C1  33
#define NOTE_CS1 35
#define NOTE_D1  37
#define NOTE_DS1 39
#define NOTE_E1  41
#define NOTE_F1  44
#define NOTE_FS1 46
#define NOTE_G1  49
#define NOTE_GS1 52
#define NOTE_A1  55
#define NOTE_AS1 58
#define NOTE_B1  62
#define NOTE_C2  65
#define NOTE_CS2 69
#define NOTE_D2  73
#define NOTE_DS2 78
#define NOTE_E2  82
#define NOTE_F2  87
#define NOTE_FS2 93
#define NOTE_G2  98
#define NOTE_GS2 104
#define NOTE_A2  110
#define NOTE_AS2 117
#define NOTE_B2  123
#define NOTE_C3  131
#define NOTE_CS3 139
#define NOTE_D3  147
#define NOTE_DS3 156
#define NOTE_E3  165
#define NOTE_F3  175
#define NOTE_FS3 185
#define NOTE_G3  196
#define NOTE_GS3 208
#define NOTE_A3  220
#define NOTE_AS3 233
#define NOTE_B3  247
#define NOTE_C4  262
#define NOTE_CS4 277
#define NOTE_D4  294
#define NOTE_DS4 311
#define NOTE_E4  330
#define NOTE_F4  349
#define NOTE_FS4 370
#define NOTE_G4  392
#define NOTE_GS4 415
#define NOTE_A4  440
#define NOTE_AS4 466
#define NOTE_B4  494
#define NOTE_C5  523
#define NOTE_CS5 554
#define NOTE_D5  587
#define NOTE_DS5 622
#define NOTE_E5  659
#define NOTE_F5  698
#define NOTE_FS5 740
#define NOTE_G5  784
#define NOTE_GS5 831
#define NOTE_A5  880
#define NOTE_AS5 932
#define NOTE_B5  988
#define NOTE_C6  1047
#define NOTE_CS6 1109
#define NOTE_D6  1175
#define NOTE_DS6 1245
#define NOTE_E6  1319
#define NOTE_F6  1397
#define NOTE_FS6 1480
#define NOTE_G6  1568
#define NOTE_GS6 1661
#define NOTE_A6  1760
#define NOTE_AS6 1865
#define NOTE_B6  1976
#define NOTE_C7  2093
#define NOTE_CS7 2217
#define NOTE_D7  2349
#define NOTE_DS7 2489
#define NOTE_E7  2637
#define NOTE_F7  2794
#define NOTE_FS7 2960
#define NOTE_G7  3136
#define NOTE_GS7 3322
#define NOTE_A7  3520
#define NOTE_AS7 3729
#define NOTE_B7  3951
#define NOTE_C8  4186
#define NOTE_CS8 4435
#define NOTE_D8  4699
#define NOTE_DS8 4978