How self-checkout took over our favorite stores — and how it's upending the way we shop

• Self-checkout has become ubiquitous over the past few decades — as have its frustrations.
• The kiosks are usually a help for both shoppers and retailers, but there's much room for improvement.
• Here's what's changing in stores' self-service lanes.

Since the introduction of self-checkout more than 30 years ago, the technology has become ubiquitous in stores across the US and around the world.