Some San Francisco Safeway stores added gates barring shoppers from leaving unless they scan a receipt. It's an anti-theft measure that has spread across the UK.

• Safeway has installed receipt-scanning gates at some supermarkets in the San Francisco Bay Area.
• The gates are meant to deter theft at self-checkout.
• The technology has already been rolled out at multiple UK retailers, and shoppers are skeptical.

Some California Safeway stores have installed security gates around self checkouts that won't open unless shoppers scan their receipts.

The gates are a theft-deterrent that's already widely used in the UK and could become more common in the US.