Smart glasses company North has told customers that their $600 (£460) purchases will stop working in a few days' time.

The Canadian company, recently purchased by Google, says its Focals glasses will cease functioning on Friday.

From then, owners will not be able to use "any features" of the glasses, or connect to the companion app.

But the company has also said it will automatically refund all customers.

It promised to send the purchase price back to the original payment method, and to contact those customers whose refunds it could not process.

At the end of June, North announced it was being acquired by Google, and would not release a planned second-generation device.

It also said it would "wind down" its first generation smart glasses, released last year.

Customers found out that meant the smart glasses would be rendered "dumb" through a statement published on the company's website and by email.

The Focals glasses, however, come with prescription lenses as an option, meaning they can function as everyday prescription eyewear. The bulky frames, housing a laser, battery, and other kit will no longer do anything that regular spectacles cannot do.

Ben Wood, chief analyst at CCS Insight, said the pulling of features from cloud-powered hardware is not uncommon - and something that has happened to him before.

"If you want to be an early adopter and have some fun new tech that an ambitious start-up has created, there's always a risk that they won't be able to make the business plan stack up," he warned.

"That could either mean the service stops working or you end up finding you have to pay additional charges to maintain service continuity."

Not-so-smart homes

There have been several examples of internet-enabled smart devices that are suddenly rendered "dumb", losing many features or even becoming unusable when the company changes its business model.

For example:

• Friendly home robot Jibo started telling its owners that its servers were being shut down and its reactions would "be limited" afterwards - though more than a year later, it is still working
• Speaker firm Sonos had to reverse plans to "brick" older smart speakers, which will no longer receive updates and eventually stop working
• Smart home platform Wink recently announced that previously free features would be locked behind a monthly subscription, limiting functionality
• This week, it was announced the Mellow $399 sous-vide cooker will lose its smart functionality without a $48-a-year subscription.

Google made an early but ill-fated attempt to make smart glasses mainstream with its Google Glass product in 2013.

When it bought North, Google said the company's "technical expertise" would help it realise its vision of an "ambient computing" future.

And despite the short notice, Mr Wood says the offer of a full refund for North customers is "exceptionally generous", and the best approach from a customer relations point of view.

"For Google, given the small number of North glasses that were actually sold to real end users, it's a rounding error," he said.

"But not all people who invest in startups will be that lucky."