When hundreds of 999 calls came in from fans at the Download festival two years ago, the emergency services must have thought a disaster was unfolding at the three-day heavy metal gig in Leicestershire.

In fact, the calls were made automatically from smartwatches and other devices worn by fans because “the tech assumed that people in moshpits had been in a collision”, according to Leicestershire police.

Now the force is appealing to those attending the festival this weekend to turn their devices to airplane mode or disable emergency alerts to avoid unnecessary 999 calls.

The number of 999 calls during the event doubled from the usual 600 or so over a long weekend.

“In previous years, due to wearable tech issues, we saw a rise of nearly 700 extra 999 calls in a weekend,” Leicestershire police said on social media this week. “All those calls had to be assessed … to ensure there is no threat, risk or harm, taking our contact handlers away from answering true emergency calls.”

Police are asking fans to stay on the line if their device makes an accidental 999 call, or to answer callbacks made by emergency teams “to let us know you are safe”.

According to one US personal injury law firm, moshpits “always have risks and dangers” but can result in “enjoyable chaos and energy release”.

Some wearable technology includes a “crash detection” feature. Apple says its watches and some iPhones will sound an alarm and display an alert if they detect a “severe car crash”. Unless the alert is cancelled, the device calls the emergency services after a 30-second countdown.

About 75,000 people are expected to attend the Download festival in Donington Park, a racetrack near Castle Donington in Leicestershire, for what the organisers call the “UK’s premier rock festival”.

The site has been open to campers since Wednesday with the rock festival opening on Friday. Green Day, Sleep Token and Korn are the daily headline acts at the festival.

This year’s fancy dress theme is Friday 13th.

The organisers said: “For everyone’s safety and comfort, we ask that you don’t bring any fake or replica weapons, including toy guns, swords or other realistic-looking props. These items can cause confusion during security checks and may be mistaken for real weapons by our teams or the police. They can also be distressing to other festival-goers.”