New Delhi, Dec 4 (IANS): Wearable brand Fitbit has offered replacements for some users of its Sense smartwatch after it discovered a bug in the electrocardiogram (ECG) feature that affected the readings, the media reported on Friday.

The company has sent emails to the affected users warning that the devices are affected by an unspecified "hardware issue".

Fitbit that has been acquired by Google for $2.1 billion introduced the ECG feature in the $329.95 Sense smartwatch in October that reads heart rhythm for conditions like atrial fibrillation (AFib).

According to a report in The Verge, Fitbit has confirmed that the bug specifically affects the ECG functionality on a limited number of devices.

"Thanks for your purchase of Fitbit Sense. We identified a hardware issue with your device that could affect its ability to work properly. Please return the device to us. We'll provide you with a prepaid return label," the email read.

The affected users will be given a replacement device free of charge.

"The problem means the app can incorrectly display an "inconclusive" result during readings.

"Fitbit confirmed that no other devices, or future Sense smartwatches shipments, are affected by the issue," the report said.

The smart wearable brand sold 3.3 million devices at an average selling price of $104 per device in the third quarter that ended on October 3.

The company has introduced several new devices in the past 12 months, including Fitbit Charge 4, Fitbit Sense, Fitbit Versa 3 and Fitbit Inspire 2 -- representing 52 per cent of revenue.

According to new data from the International Data Corporation (IDC), Fitbit and the Indian consumer electronics brand BoAt tied for fifth place in the third quarter, each holding 2.6 per cent of the global wearables market.

"Fitbit's new devices launched near the end of the quarter were relatively well received and a price drop on older models has helped the company stay within the Top 5," the IDC report said.