Why do curling stones have batteries? And other questions answered

Posted at 2:07 AM, Feb 04, 2022

Curling stones explained

Curling isn't a new sport to the Olympics, but sometimes it can seem like one of the most complicated. If you've watched any mixed doubles games so far, you may have some questions about what you've seen. We'll attempt to explain curling stones and answer some of those other questions here.

Why do curling stones have batteries?

This question came up during Team USA’s second game of the 2022 Olympics against Italy, when Italy’s Stefania Constantini was charged with a hogline violation in the sixth end. Constantini realized she had made an error when a red light flashed as she released the stone.

Each curling stone is equipped with a heat sensor that can sense if a player releases the stone too late - past the hogline - for a violation. So, stones have batteries to power the sensor.

SEE MORE: Italy defeats Team USA in mixed doubles curling

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So what do the lights on the stone mean?

If the stone lights up green, that means it was a legal throw. If the light is red, it was a hogline violation, and the stone cannot be played. It must be taken off the ice.

What is the hogline?

The hogline is the red line that stretches across the ice on both ends. When a team is throwing stones, they must release the stone before passing the line or it’s a violation.

SEE MORE: Curling 101: Glossary

What is a curling stone made of and how much does it weigh?

In the official USA Curling rulebook, each curling stone can be no greater than 44 pounds in weight, and no less than 38 pounds. That weight includes the handle.

Each stone can have a circumference no greater than 36 inches, and much be less than 4.5 inches in height.

Stones are made of granite. According to, each stone used in the Olympics is made of a special granite found on the island of Ailsa Craig in Scotland.

The Ailsa Craig granite is some of the hardest and purest found in the world and maintains its shape despite the moist, wet conditions of the ice surface curling is played on.

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How long is a curling ice sheet?

The official USA Curling rulebook states the length of the ice sheet from the inside edges of the back boards is 150 feet. The width of the sheet is a maximum 16-feet, 5-inches.

SEE MORE: Curling 101: Equipment

What is a power play?

Power plays are only available in mixed doubles curling. In mixed doubles, each team starts with one stone in play before throwing begins - One team will place a stone in the house, and the other will place one as a guard.

But when a power play is used each stone is moved to the side, with the inside stone sitting on either the 8-foot or 12-foot line, and the guard stone away from the center of the ice.

Each team has one power available per game.

In mixed doubles curling, can both players sweep?

Yep! Though it doesn’t happen often.

Typically, the person who throws will stay back and serve as a guide for the sweeper.