Grocery store prices are changing faster than ever before — literally. This month, Walmart became the latest retailer to announce it’s replacing the price stickers in its aisles with electronic shelf labels. The new labels allow employees to change prices as often as every ten seconds.

“If it’s hot outside, we can raise the price of water and ice cream. If there's something that’s close to the expiration date, we can lower the price — that’s the good news,” said Phil Lempert, a grocery industry analyst.