In my experience, capnography is usually an accessory output available on a lot of commercial (and relatively expenseive) pulse oximetry machines. In a resuscitation scenario, the lack of a pulse doesn't necessarily mean the heart isn't working. A minimal level of end tidal CO2 concentration of expired air can indicate that exchange is in fact taking place in the lungs/pulmonary vasculature regardless of the presence of a pulse. This CO2 level has been used to predict outcome and help decide when to terminate resuscitation in such events.

Like pulse oximetry, capnography typically works by detecting infrared energy absorption at a specific wavelength compared to a reference energy source. One difficulty with the idea of making a cheap device that one might, for example, plug into a smart phone, is that unlike a pulse oximeter, you don't simply slip the energy source/detector over someone's fingertip - the capnographic sensor is usually adapted or otherwise attached to the endotracheal tube with which the person in extremis is intubated.