Like many people, I spend most of the week sitting at a desk, worrying about deadlines and emails. There are plenty of fitness devices that track your movement during the day. But how about your stress levels? Recently, I tested two devices, Tinké by Zensorium and Inner Balance by HeartMath, that use biofeedback to do just that.

Tinké is a palm-size sensor that costs $100 and monitors your cardiorespiratory health using an iPhone or iPad. When I plugged it into my iPhone, a message on the screen prompted me to download Tinké's mobile app. Next, I placed my thumb on the sensor, and the app displayed my heart rate, blood oxygen level, respiration rate, and heart rate variability (i.e., changes in the rate at which your heart beats). The app compiled the data into a fitness score--called a Vita Index--that I could share with Facebook friends and Tinké users. I could also gauge my stress level, or Zen Index, by completing a 60-second breathing exercise that involved breathing in time with expanding and contracting circles.

The initial results were alarming. My Vita Index was a dismal 62 out of a possible 99, and my Zen Index was 46 out of 99. After seeing my scores, I was more stressed out than ever. Over the next week, I checked my vitals and did my breathing exercise three times a day. Noting that my stress levels shot up before big phone calls, I spent five minutes breathing in and out slowly beforehand. By the end of the week, my Vita Index jumped to 90, and my Zen Index rose to 56.

Next, I tested Inner Balance, a $99 kit that includes an app for the iPad, iPhone, or iPod Touch and a sensor that clips to your earlobe. I plugged the sensor into my iPhone using an included cable and downloaded the app. To start a session, I selected my desired length of time (five minutes) and identified my mood (content). Then, I began a guided breathing exercise, breathing in time with an expanding and contracting circle, much like with Tinké, while thinking about a positive moment. A line representing my variable heart rate fluctuated up and down as I breathed, and a "coherence" score measured my heart rate stability.

On the app, I could look at photos with positive associations and listen to relaxing music. I could also share the results with other Inner Balance users and track my progress. Not surprisingly, my initial coherence score was an awful .5 out of 15. But after doing the breathing exercises three times a day for a week, my score jumped as high as 8.5, averaging about 4.5.

I was skeptical when I started my experiment. But both products helped me control my stress levels without doing much more than breathing. In the end, I wound up preferring Tinké, mostly because the Inner Balance earlobe sensor was a bit pesky to wear. I still spend most of the day at my desk, but now I'm much more relaxed.