The Fitbit (see "Heart Rate Part 4...") and AliveCor's Kardia are the only consumer units I know of that provide heart rate trends. Whereas my cardiologist will not take seriously the information my Fitbit provides, he said (because of the technology employed by the Kardia to take heart rate) he would take notice if I could provide him with information taken from AliveCor's Kardia.
Unfortunately, because the Kardia is capable of recording heart rate for no longer than five-minute periods the unit is unacceptable for my purposes.
Can someone explain how the Kardia works and speculate why it only works for such short periods?