Are consumer heart rate monitors really accurate?

There are many devices on the market today that claim to be able to track your heart rate wherever you go. But how do they compare to what a doctor can measure with an EKG or an old-fashioned pulse reading?

CNET reporter Sharon Profis and Kaiser Permanente cardiologist Dr. Jonathan Zaroff tested five fitness trackers currently on the market. For each test, Profis got three heart rate readings at rest and three after running on a treadmill.

EKG is the gold standard for measuring heart rate using electricity sensors to detect the small pulses of electricity that drive every beat of the heart.

One of the consumer devices tested, the Garmin Vivofit, has a chest strap that connects wirelessly to a wrist strap. According to Zaroff, the Garmin Vivofit "chest straps essentially have an EKG leed over the chest. So it's the same technology. " The device was accurate at resting and exercising heart rates. It can be used to measure heart rate while exercising.

The other four devices in the test use optical sensors on the wrist or fingertip and only work standing still. Zaroff observes, "An optical sensor is not near your heart. It's sensing the flow of blood through your capillaries, one pulse per each heart beat."

The Withings Pulse O2 has a clip with a removable fingertip pulse monitor. Though it was accurate at resting pulse rates, it couldn't keep up with Profis's heart rate when exercising.

Basis Carbon Steel and Samsung Gear Fit are both wrist bands with built-in optical sensors. They were accurate at resting rates in the test, but couldn't keep up with rapid heart rates either.

The Samsung Galaxy S5 phone comes with a built-in optical sensor to sense fingertip pulse and was accurate even at a heart rate of 190.

Zaroff warns that these devices are not going to be useful for everyone: "If someone is very out of shape and beginning to exercise... an intermittent device like that might be pretty good for a while. Someone very fit might find it very disappointing."

The monitors are currently not regulated by the Federal Drug Administration because they are not considered medical devices.

When asked about inaccuracies by CNET, Basis and Withings offered replacement devices and expressed confidence in their technologies. The Samsung Gear Fit manual notes that inaccuracies may be due to measurement conditions and surroundings.

Read more on CNET for a complete list of test results.