On it are a range of products for sale. And the capabilities of the products on that page can now be found in a single place: inside your smartphone.

The list includes a "VHS Camcorder" (remember those?), "mobile cellular telephone" (that just made calls), a 20-memory speed dial phone (with a cord), a tape recorder, scanner and CD player. Oh, and a desktop computer.

The total value of that page, in 1991 dollars, was $3239. If you bought a smartphone at any time in the past couple of years, you paid less than a quarter of that price - in 2017 dollars, no less. For far, far, superior technology.

(Remember that next time someone complains that things aren't getting better, or that everything is so expensive these days.)

Sticking with the theme, Radio Shack filed for bankruptcy in 2015. And again in 2017.

That catalogue page, though, is both a metaphor and an all-too-real example of something every investor should be alert to: the potential disaster around the corner. It's exemplified in a simple phrase: "When your product becomes someone else's feature."

Sure, some people still buy portable CD players that clip to their belts. Or bulky VHS camcorders.

When was the last time you saw more than two people at the same spot using an old-style photographic camera? And even if you did, they were likely swamped 50 to one by smartphones taking snaps, right?

The miniaturisation of technology, which means we each carry around more computing power in our pockets than was in the first few generations of spacecraft, is largely responsible for this shift. But not entirely.

Email, free with any internet connection, has devastated traditional post. Improved vehicle security and in-car audio systems have all but destroyed the car alarm and after-market stereo businesses. The international linking of debit and credit card systems has meant you no longer need traveller's cheques in your wallet next to your Bankcard (also gone). There are many, many additional examples.

And, back to computing, Amazon, Apple and Google are trying to take it to the next level. Amazon's new Prime "club" includes free streaming of a host of movies and music. Apple and Google's music subscription programs make albums - either physical or digital - an endangered species.

Then there's the smartphone app stores. Apps, though you do have to pay for some of them, have replaced GPS units (which themselves replaced physical maps), stream television shows and sport, allow you to buy goods online, play games - oh, and make phone calls.

One of the newer inventions to really take hold recently, though, is the ability to use your phone to pay. I've just been away for a week, and all but one transaction was done by tapping my phone against the payment terminal. For now, I'm linking it to my credit cards. But how long before the likes of Visa and American Express face disruption of their own?

That product, the credit or debit card, is quickly becoming a feature. And not only of the smartphone but of the operating system.

Even better (or worse, if you face disruption): the operating system itself is becoming part of a bigger ecosystem. If you're part of Team Google, for example, your phone, computer files, payments, email and a whole lot more are inside one ecosystem. Ditto for Apple. So when one of them releases a new feature ???

Innovation is happening at a greater rate than ever before. Products are becoming features at a rate of knots. Businesses that once seemed impervious to the march of technology are increasingly under threat by digitisation. And with it, by globalisation.

How will our local banks tackle the deluge of online payment options such as PayPal, Apple Pay or Android Pay? Will Amazon's arrival spell trouble for not only discretionary retailers such as Harvey Norman and JB Hi-Fi, but also Woolies and Coles?

Because here's the rub: companies don't fall over when the last customer walks out the door.

They face trouble when 10 per cent of customers leave. Because they have massive infrastructure - store footprint, inventory, administrative staff, marketing and other costs - that doesn't deal well with declining sales.

Just ask Radio Shack. It did more than $US4 billion in sales in the last year it made a profit. It fell to a loss when revenue hit $US3.8 billion. And it never recovered.

The old rules of market dominance no longer apply. Not every company faces Radio Shack's fate, but every investor - not just in the technology arena - should be vigilant to their company's product becoming someone else's feature. It could be the beginning of the end..

Scott Phillips is the Motley Fool's director of research. He owns shares in Amazon.com.