Early adopters of the Apple Watch, Apple Inc's first new product in five years, are complaining that a number of its key functions are disrupted by their tattoos.

Tattooed owners of Apple Watch have found that their inked skin confuses the sensors on the underside of the device.

One Reuters reporter, Matt Siegel, demonstrated the issue on his 42mm version with stainless steel case and black classic buckle, which cost A$1,029 ($822).

He has a tattoo on one wrist and found his watch locks on tattooed skin and does not deliver the soft pings that alert a user to incoming messages.

"I should be turning my wrist and every time I look at the watch I should be seeing the time of day. Once it's on my wrist once and unlocked it should stay that way, it shouldn't be locking itself ever single time," he said.

The heart rate readings were also significantly different on the tattooed and untattooed wrists.

An Apple support article says the watch uses green LED lights paired with light-sensitive photodiodes to detect the amount of blood flowing through the wrist and calculate the frequency of heart beats.

A spokesman for Apple in Sydney declined to comment on Thursday (April 30), but three Apple employees at its flagship Sydney store, including a senior advisor from its tech support line, said they were unaware of any issue.

A website support page from the company says tattoos can interfere with readings from the heart rate monitor, but does not mention interference with other functions.

"Permanent or temporary changes to your skin, such as some tattoos, can also impact heart rate sensor performance. The ink, pattern, and saturation of some tattoos can block light from the sensor, making it difficult to get reliable readings," it said.