They quantify your stress level by calculating your heart rate and the minute variations in the time between each beat, a measurement known as heart rate variability (HRV), which has been used to gauge the likelihood of mortality after a heart attack and to help assess certain psychiatric conditions.

WSJ: Keep Calm and Carry a Gizmo

While there are many heart rate apps available, Inner Balance is monitoring heart rate variability (HRV) - a measurement of beat-to-beat changes that occur within heart rhythms and a sophisticated and highly sensitive observation of emotional fluctuations.

ENGADGET: HeartMath unveils Inner Balance iOS app and sensor for managing stress, clearing the mind

"Besides life-saving applications in fire and rescue, the potential to record dynamic scenes of a human body could have a variety of other biomedical uses including studying or monitoring breathing, cardiac beat detection and analysis, or measurement of body deformation due to various stresses during exercise, " Ferraro says.

ENGADGET: Infrared holography lets rescuers see people through walls, fire, walls of fire (video)