Amazon Dash makes shopping easier - but will it save you money?

Your fridge can now automatically order more milk when it notices you're running low, thanks to a new service from Amazon.

With Amazon Dash, customers can reorder basic household items with a single button press - and, if they have smart devices such as fridges, washing machines and printers, can even get their appliances to order food, washing powder or ink cartridges for themselves.

To start with, Dash Buttons - small wifi-connected devices - will be available for 40 brands, from Air Wick to Whiskas. They cost £5 per button, although the cost is refunded with the first order. You'll also need an Amazon Prime account.

The idea is that you'll leave one near your dishwasher, for example, and press it whenever you notice that you're running low on tablets. There's a safeguard against over-ordering: once an order's been placed, you can't make another until the first is delivered. You also get a notification when an order's placed, so you can cancel any mistakes.

"We've all experienced the frustration of running out of something we need—Dash Button and Dash Replenishment Service are designed to make that moment a thing of the past," says Daniel Rausch, director of Amazon Dash.

"Dash Buttons offer the convenience of one-click shopping from anywhere in the home — they can be placed near those frequently used items you don't want to run out of, and when you see supplies running low, the Dash Button makes it easier than ever to order more. Just press the button and your item is on its way."

Meanwhile, the Amazon Dash Replenishment Service (DRS) means connected devices can automatically reorder physical goods from Amazon. While the service isn't up and running yet, Bosch, Siemens, Grundig, Samsung and Whirlpool are working to include it.

"By integrating the Home Connect app with Amazon Dash Replenishment, customers have one less thing to worry about," says Mario Pieper, chief digital officer at BSH Home Appliances Group.

"Through Dash Replenishment, Bosch and Siemens dishwashers with Home Connect function can automatically reorder dishwasher tablets — so you never run out."

However, it's worth remembering that all this convenience can come at a cost. It makes impulse buying incredibly easy, for a start.

And of course Amazon isn't always the cheapest online option, meaning that you won't always get as good a deal as you might by shopping around. On top of this, prices on Amazon itself can vary day by day.

Finally, each button is dedicated to one particular brand; fine if you'd never buy anything else, but not if you're open to alternatives.

Finally, you have to ask yourself whether you'd actually use the buttons if you had them. In the US, where Dash has been available for some time, they aren't being used as much as you might think.

"Among the current button line-up available for purchase, fewer than fifty percent of people that bought Dash Buttons actually made an order," says Leslie Warshaw of Slice Intelligence.

"On average, Dash Button users order items about once every two months."