A new iPhone app allows consumers to compare grocery prices at supermarkets such as Asda, Sainsbury's and Tesco - on their mobile phones.
You can also use the app to scan barcodes while you're shopping to check whether the item is cheaper elsewhere.
The MySupermarket website and app allows you to compare the prices of groceries and household items at Asda, Ocado, Sainsbury's, Tesco and Waitrose.
It offers discount vouchers and deals that could help you save money on your food shopping bill. It also offers a cashback scheme and will submit your online grocery shopping order.
The new app gives you access to all of this when you're on the move, via your mobile phone. You can use the barcode scanning feature to compare prices when you're in the supermarket aisles to make sure you're getting the best price.
The cost of food and household items in supermarkets fluctuates constantly - including online. This makes it hard to see which online supermarkets offer the lowest prices over time.
So Which? has tracked the price of 100 popular branded items for 12 months at five online supermarkets and calculated average prices. You can see which online supermarket is cheapest overall in our guide to