For years, Apple's clout in the electronics world could be gauged by how easy it was to bump into devices tailor-made for a connection to an iPhone or iPod.
Hotels outfitted guest rooms with alarm clocks containing a telltale wedge of 30 tiny pins that could play music from Apple's devices and charge their batteries. Retail stores were thick with sound docks and other speaker systems meant to work with Apple gadgets.
But Apple's iron grip on the digital accessories in hotel rooms, store shelves and living rooms is starting to slip—potentially risking the royalties it earns from accessory makers and, more significant, giving Apple customers more freedom to switch to rival products. That could be an issue for a company whose stock has been shaken in recent months as investors worry that the iPhone business is slowing.
Jeremy Horwitz, editor in chief of iLounge, a Web site devoted to Apple accessories, said Apple's aggressive control over accessories for its products drove many makers to more open means of connecting devices, which helped feed the success of mobile devices made by other companies.
"At some point Apple's obsession with having control over everything that is associated with its products may wind up biting it," Mr. Horwitz said.
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The Bluetooth standard for wireless connections has allowed accessory makers to build products that can work with many kinds of devices because they no longer have to worry about a physical hook. Other phone makers like Samsung and tablet-computing device makers like Amazon have become strong alternatives in the eyes of gadget shoppers. And Apple itself provided an opening for competitors when it changed the way its phones connect to other devices, aggravating both its business partners and consumers.
Now accessory makers are eager, even obliged, to think beyond Apple.
"We've had to adapt to new technology, support more devices and meet the growing demands of consumers looking for accessories that can accommodate multiple devices," said Ezra S. Ashkenazi, chief executive of iHome, one of the biggest makers of iPhone clock radios and other Apple audio accessories. This year, iHome is releasing more products with Bluetooth than ever before, he said.
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Apple says it is fine with the wireless direction in which accessories are headed. "Apple provides users with the best wired and wireless connectivity options to work with the broadest range of accessories," said Tom Neumayr, a spokesman for Apple. "As a result, iOS users have access to the world's largest ecosystem of options and the most seamless integration with our products."
Apple expected some grumbling from customers and partners last fall when it introduced in the iPhone 5 a new way for the mobile phone to connect to other devices. But its executives defended the connector, Lightning, because the new, smaller design allowed for slimmer phones and tablets. While the 30-pin connector can be plugged into an old iPhone in only one way, a Lightning cable works even if it is flipped over.
Apple did not tell accessory makers about the change ahead of time, which is normal for a company known for its secrecy, but it was painful for many of its partners.
"You really don't know where Apple is going to go next, if they're going to change to something else down the road," said Kyle Thompson, director of marketing for Cambridge SoundWorks. "They've made a lot of companies like us really nervous."
That change frustrated partners whose customers had invested in products that used Apple's old 30-pin connector. Those older devices are incompatible with the latest Apple products without an adapter that Apple sells for $29 to connect to the latest Apple products. Also, the new Lightning connectors are more expensive to license and manufacture than the old ones, electronics makers say.
"A lot of us were bitten pretty badly by the connector transition," said Ian Geise, senior vice president for marketing and product development at Voxx Accessories Corporation, which makes audio products under RCA, Acoustic Research and other brand names.