The Apple Watch has been available in extremely limited quantities since pre-orders for the device launched on April 10, and a new report from The Wall Street Journal sheds some light on why supplies have been low. A key component of the Apple Watch, the Taptic Engine, was made by two separate suppliers, and the devices created by one of Apple's suppliers were "found to be defective."

After mass production began in February, reliability testing revealed that some taptic engines supplied by AAC Technologies Holdings Inc., of Shenzhen, China, started to break down over time, the people familiar with the matter said. One of those people said Apple scrapped some completed watches as a result.

Apple was unable to use the Taptic Engines from the supplier in Shenzhen, China, but those produced by a second supplier in Japan did not have the same issue. The majority of Taptic Engine production is now being done in Japan, but it will take some time for the factory to increase production, and with a single supplier, quantities of the taptic engine available for use in Apple Watch devices likely remains low.



The Taptic Engine is a linear actuator, creating motion in a straight line by moving a small rod. It powers the haptic feedback capabilities of the Apple Watch, delivering the small taps that are felt on the wrist with notifications, pings from friends, heartbeats, and more. The Taptic Engine is a major part of the Apple Watch, working in conjunction with audio cues to deliver subtle alerts and notifications to Apple Watch wearers.

To resolve some of the supply constraints on the Apple Watch, Apple is said to be planning to add Foxconn as a second assembler of the Apple Watch, alongside Quanta Computer. Foxconn may begin manufacturing the Apple Watch in late 2015 at the earliest, so according to The Wall Street Journal, it may take several months for Apple Watch supplies to improve significantly.

Apple has repeatedly said that it's working to get Apple Watch orders as out as quickly as it can, and it has indeed been shipping orders out before their prospective delivery dates. Many customers who originally had 4 to 6 week shipping estimates have already begun receiving their devices.

Apple Watch orders placed today offer shipping estimates ranging into June and beyond, but it's possible that many orders will reach consumers ahead of that time as Apple works to increase available supply.