Heart rate can be measured with a wide range of equipment, from a simple stethoscope to clinical-grade electrocardiographs to the smartwatch on your wrist. Each device uses a different method to detect your pulse, and the accuracy varies significantly depending on the technology and where on your body the measurement is taken.
Electrocardiograph (ECG or EKG)
The electrocardiograph is the gold standard for heart rate measurement. It works by detecting the electrical signals your heart generates with every beat. Those signals travel through your body and can be picked up on the skin’s surface using small adhesive electrodes, typically placed on your chest and limbs. The machine records this electrical activity and displays it as the familiar wave pattern on a screen or printout.
A standard 12-lead ECG uses 10 electrodes placed at specific points on your body to create 12 different “views” of the heart’s electrical activity. This gives clinicians not just your heart rate but detailed information about rhythm, conduction, and potential damage. In a study published in JAMA Cardiology comparing various devices, the ECG served as the reference against which all other heart rate monitors were judged.
Portable Heart Monitors
When a standard ECG isn’t enough because symptoms come and go, portable monitors extend the recording window. A Holter monitor records your heart’s electrical activity continuously, typically over 24 to 48 hours. An event monitor works differently: it can be worn for a month or longer and records only when you press a button to activate it during symptoms, or when it automatically detects an abnormal rhythm.
There are two main types of event monitors. A symptom event recorder captures several minutes of data after you activate it. A memory looping monitor goes a step further, storing data from a few minutes before activation as well, so it captures what your heart was doing before, during, and after the episode. According to Johns Hopkins Medicine, these devices use sensors attached to your chest with sticky patches, connected by wires to a small monitor you can clip to your belt or slip into a pocket. Some simpler models are handheld or wrist-worn and don’t require chest sensors at all.
Pulse Oximeters
The small clip that goes on your fingertip at the doctor’s office is a pulse oximeter, and it measures heart rate as a secondary function alongside blood oxygen levels. It uses a technology called photoplethysmography (PPG): an LED shines light through your skin, and a sensor on the other side detects how much light passes through. With each heartbeat, blood pulses through tiny vessels in your finger, changing how much light is absorbed. The device counts those fluctuations to calculate your pulse.
This same optical principle powers most consumer wearables, though pulse oximeters tend to be more accurate because the fingertip has a dense, superficial network of blood vessels that produces a strong signal.
Smartwatches and Fitness Trackers
Wrist-worn devices like Apple Watch, Fitbit, and Garmin models use the same light-based PPG technology as pulse oximeters, but adapted for the wrist. Green LEDs on the back of the device flash hundreds of times per second, and photodetectors measure how much light is reflected back. Blood absorbs green light effectively, so each heartbeat creates a measurable dip in the reflected signal.
Accuracy varies by brand and activity level. A JAMA Cardiology study found that the Apple Watch had a concordance correlation of 0.91 with a clinical ECG, while the Fitbit Charge HR scored 0.84. All wrist-worn monitors performed best at rest and became less reliable during exercise. Some devices underestimated heart rate during vigorous activity by 6 to 7 beats per minute, while others overestimated during moderate exercise by up to 9 beats per minute. The Polar H7 chest strap, which uses electrical sensors rather than optical ones, scored 0.99, nearly identical to an ECG.
Chest Strap Monitors
Chest straps are the most accurate consumer-grade heart rate monitors available. Unlike wrist-based devices, they detect the actual electrical impulses from your heart, similar in principle to an ECG. Two electrode pads built into the strap sit against your skin just below the chest muscles and pick up the tiny voltage changes that occur with each heartbeat. The strap transmits data wirelessly via Bluetooth or ANT+ to a paired watch, phone, or gym display.
The tradeoff is comfort. Many people find chest straps less convenient than a wristwatch, which is why optical wrist sensors have become dominant in the consumer market despite their lower accuracy.
Smart Rings
Smart rings from companies like Oura use the same PPG light sensors found in smartwatches, but placed on the finger instead of the wrist. This turns out to be a meaningful advantage. A 2022 review in Frontiers in Physiology found that fingers produce more accurate heart rate readings than wrists because they have a denser network of blood vessels located closer to the skin’s surface.
Smart rings may also be more accurate across different skin tones. One of the known limitations of optical sensors is that melanin in the skin can absorb some of the light meant for the sensor, distorting readings. A 2023 study in Mayo Clinic Proceedings: Digital Health noted that there is generally less melanin on the palm side of the finger than on the wrist, which could reduce this source of error.
Blood Pressure Cuffs
If you’ve used an automatic blood pressure monitor at home or in a pharmacy, you may have noticed it also displays your pulse. These devices detect heart rate as a byproduct of measuring blood pressure. The cuff inflates to compress the artery in your upper arm, then slowly deflates. As blood begins flowing through the artery again, it creates small pressure oscillations inside the cuff with each heartbeat. The device’s processor counts these oscillations to determine your pulse rate while simultaneously calculating your blood pressure from their pattern.
Gym Equipment Grip Sensors
Treadmills, ellipticals, and stationary bikes often have metallic hand grips that read your heart rate when you hold them with both hands. These sensors detect changes in blood flow through your palms using a mild electrical signal that passes from one hand to the other through your body. They’re convenient for a quick check during a workout, but they require you to grip the handles firmly and hold still for several seconds, and they’re generally less accurate than a chest strap or wrist monitor.
Stethoscopes
The most basic tool for measuring heart rate is a stethoscope, which has been a clinical staple even longer than the ECG. A clinician places the flat diaphragm side of the stethoscope against your chest and listens to the two heart sounds produced by your valves closing with each beat. Counting those paired sounds over 15 or 30 seconds and multiplying gives your heart rate. It requires no batteries, no calibration, and no software, but it does require a trained listener and only provides a snapshot.
Smartphone Cameras
Your phone’s camera can estimate heart rate using a technique called remote photoplethysmography (rPPG). When your heart beats, the rush of blood through tiny vessels near your skin causes color changes so subtle they’re invisible to the naked eye. A camera can detect these shifts, particularly in the green light spectrum, because hemoglobin in your blood absorbs green light more than red. Some apps ask you to place your fingertip over the camera lens, while others analyze your face through the front-facing camera without any contact at all.
This technology works because blood circulating through the external carotid artery during heartbeats creates measurable changes in facial skin color that a standard smartphone camera can pick up frame by frame. It’s a useful option when no other device is available, though it’s less reliable than dedicated hardware, especially in poor lighting or during movement.