Amazon is on the cusp of opening its cashier-less stores - but it has one major challenge to overcome

• Amazon is getting closer to opening its first cashier-less grocery store, Amazon Go.
• The store uses cameras and shelf sensors to track what shoppers remove from shelves.
• The technology accurately charges individual shoppers for purchases but still has trouble tracking groups of shoppers like families.

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Amazon is getting closer to opening its first cashier-less grocery store after months of delays, but it has one major challenge to overcome.

The store, called Amazon Go, can accurately charge individual shoppers for items they remove from shelves, but it's still unable to accurately charge groups of shoppers like families, Bloomberg reports.

Amazon has been testing the concept, which it markets as a grocery store without lines or checkouts, in downtown Seattle. It uses cameras and shelf sensors to track what shoppers pull from shelves and then charges them for what's in their carts when they leave the store, all without the use of cashiers or physical registers.

Amazon employees have been trying to fool the system though measures like wearing Pikachu costumes while shopping, according to Bloomberg.

The technology passed the costume test, but it can still be fooled by shoppers moving in groups.

Plans for Amazon Go were unveiled last December, and the first store was expected to open to the public this year. But technical difficulties have delayed its opening.

The wait shouldn't last much longer, however; the company is starting to hire construction managers who would build the first stores, Bloomberg reported.