How it works: A sensor clips to your earlobe to track your heart rate.
Real-life road test: I attached the sensor to my ear while at the office (luckily, my hair covered it or I might have felt weird wearing it at work). When a few last-minute tasks made me late for an after-work event, the app picked up on my increasing heart rate and a message on my phone prompted me to inhale and exhale along with the onscreen breath pacer. Three minutes later, my anxiety had dissipated, leaving me feeling more energized than frantic.
Good idea or bad idea: More good than bad. I appreciated the reminders—"Breathe just a little deeper"—when the program sensed I was entering stress mode before I did.