You can record your heart rate manually by holding your wrist and counting your pulse, but this hasn’t stopped technology companies producing devices to do the job with electronics. Most of these devices measure  heart data ,body temperature and blood glucose level  at in time and may record it on a smartphone app which may build up a richer set of data than you might get with a stopwatch and pencil. The most useful metrics they collect are your RHR (resting heart rate) a reading taken when you are relaxed,blood pressure ,blood glucose level  most typically first thing in the morning.