High error percentage in Sensor data

This article explains how to fix a high error percentage in Firstbeat Sports Sensor data.

Symptom

Measurements show a high error percentage, which appears as poor data quality. Since 12 June 2026, measurements are no longer discarded because of a high error percentage. To understand what the percentage means and when the results are affected, see Measurement error and heart rate data quality explained.

Cause

• The Sensor kept recording after the session and recorded an error-filled tail.
• The HR strap is dry, loose, badly positioned or worn out.
• One Sensor pin is loose, or the Sensor is attached upside down.
• Some shirts and sports bras create static electricity. Dry, synthetic clothing is the most likely to generate static.
• Sports with a lot of arm and upper body movement, for example CrossFit, tennis and handball, cause more errors.

Solution 1: Trim the extra recording

1. Trim the extra part. If the Sensor kept recording after the session, trim the extra part off in Firstbeat Sports Cloud: Measurement settings > Trim & Merge.

Solution 2: Wear the HR strap correctly

1. Moisten. Moisten both electrodes of the HR strap and the skin under the strap before the session.
2. Position the strap. Place the strap securely under the chest, not too high and not too low.
3. Tighten. Wear the strap snug: tight enough not to shift during movement, loose enough to breathe comfortably. Tighten the strap during the session if possible.
4. Let the signal stabilize. Allow 10–30 seconds after putting the strap on for the reading to stabilize. A few minutes of warm-up also helps, because sweat improves the contact between the skin and the electrodes.
5. Use conductive gel when needed. For critical use cases, use conductive gel for a stronger signal.

Solution 3: Attach the Sensor correctly

1. Check the attachment. Check that both Sensor pins snap into the HR strap and that the Firstbeat logo on the Sensor faces up.
2. Prevent the pins from popping off. If the pins have popped off before, use the Sensor protector sleeve. If the Sensor keeps popping out for an athlete, give the athlete an HR strap with a tighter attachment.

Solution 4: Change the shirt

1. Change the shirt. Ask the athlete to wear a different shirt or sports bra, preferably not dry, synthetic clothing, and check the next measurement.

Solution 5: Maintain the strap and Sensor

1. Rinse and wash. Rinse the strap after every use and wash the strap weekly, following the maintenance instructions. Hang the strap or lay the strap flat to dry, and never use a dryer.
2. Inspect. Check the strap elastic and the electrode contacts regularly for wear, and check the Sensor battery level regularly.
3. Replace worn equipment. Replace the HR strap after about 6 months of daily use, at the latest after 2 years. Replace Sensors and straps that are not in good condition.

Solution 6: Narrow down the cause

1. Swap the strap. Try a different HR strap with the same athlete.
2. Swap the Sensor. Try a different Sensor.
3. Change the location. Try a different location, for example outdoors instead of the gym, to rule out an environmental cause.

If the problem continues

If the same Sensor gives poor data with different athletes and straps, fill in the faulty device form. For other questions, ask the Customer Agent chat on this page or email support@firstbeat.com. Include as much information as possible to help us solve the issue faster.