iBiofeedback

• IBiofeedback tracks your heart rate and integrates it into healing modules that help you meditate, recite mantras or simply relax. Each module adjusts its display or auditory delivery based on changes in your heart rate. To work to its fullest extent, iBioFeedback requires an external heart rate measurement sensor. However, the application also gives you the option of tapping your heart rate on your iPhone’s screen. IBioFeedback is 195MB in size, costs around $2 and requires iOS 3.1.2 or later.
  
  

BellyBio Interactive Breathing

• BellyBio Interactive Breathing combines breathing exercises with music. The application uses the iPhone’s built-in gyroscope to monitor your breathing, providing you with instantaneous feedback in the form of stress and breathing graphs. Additional features include automatically adjusting music that responds to your breathing, customizable visuals and a variety of logging tools to track the application's duration of use, dates of use and minimum and maximum stress levels. BellyBio Interactive Breathing is a free application that’s 173MB in size and requires iOS 3.1.2 or later.
  
  

Stress Check

• Stress Check analyzes your heart rate to monitor your level of stress. The application uses the iPhone’s camera to track heart rate variability. It then takes this number and places it on a dynamic percentage scale from zero to 100. Stress Check’s features include tools to help you track your stress patterns, control them, determine their causes and share your results with friends. Stress Check is 2MB in size, costs around $1 and requires iOS 4.0 or later.
  
  

Biofeed

• Biofeed is similar to BellyBio Interactive Breathing in that it focuses on your breathing patterns and tries to help you breathe in a more relaxed manner. It works by having you place your iPhone on your solar plexus and then instructs you on how to breathe using your belly rather than your chest. As you inhale and exhale, the application analyzes the changing tilt of the iPhone and uses acoustic feedback to tell you how well you’re breathing. Biofeed is 3MB in size, costs around $2 and requires iOS 3.0 or later.