The Hövding collar's sensors can detect characteristic movements that happen in a crash and reacts by inflating the bag with helium.
With one in every four journeys being taken along its 300-mile network of cycle lanes, Sweden's third city of Malmö is often cited as one of the most cycle-friendly cities in a cycle-friendly country.
But even in a place that appears a paradise for thousands who use cargo bikes to ferry their children to school and bring home the groceries, there have been arguments over safety.
Every time any government proposes making cycle helmets compulsory, it sparks a fierce controversy; Malmö was no exception when Swedish ministers mooted a helmet law in 2005. Just one in 10 cyclists in the city wears one, according to designers Anna Haupt and Terese Alstin. The pair thought there must be a way round people's resistance to traditional polystyrene crash helmets. Wouldn't it be better to design something that cyclists would be happy to wear?
"People told us they are too bulky. 'I think it makes me look geeky', 'I don't like the way it interferes with my personal style and my hairdo' – a lot of vanity involved of course," said Alstin. "And then we just started brainstorming on how to solve all those problems for people. We started thinking about something that would not be on your head at all, in order to solve [the problem] that people wanted something that would not mess up their hair. That's what got us into thinking about airbag technology, because that is hidden most of the time until you need it and then it pops out."
After seven years of research and €13m (£10.6m) in funding, the result of their efforts can be seen on cyclists – although it can be hard to spot at first. Sitting around the neck like a snood, the Hövding collar – Swedish for chieftain – is packed with a folded airbag that inflates in a tenth of a second when the wearer is involved in an accident. With four upmarket London cycle shops now stocking the collar, the eagle-eyed may have spotted it around the UK capital.
"There are avalanche backpacks for skiers, there are vests with airbags for horseriders so it was starting to spread and we just decided that it is time for cyclists to have that protection as well," said Alstin.
For the collar to know when to inflate, the designers needed data from thousands of accidents re-enacted using dummies. At the same time, data from normal cycling where an accident was not involved was also put together and an algorithm written to differentiate the two.
Both crash scenarios and normal cycling movements were re-enacted with crash test dummies to give a bank of movement data for the device. When a cyclist turns on the Hövding, a sensor unit within the collar detects movements using gyroscopes and accelerometers – similar to technology used in smartphones and fitness bands. In the event of a crash, the sensors detect the movement and deploy the airbag.
The sensors can detect characteristic movements that happen in a crash and the device reacts by inflating the bag with helium, creating a dome over the head that leaves the face free and cushioning an impact in a similar way to a car airbag. A black box records details of the accidents for research purposes.
The collar is turned on by being zipped around the neck and attached with a clip, which prevents it accidentally triggering when not being worn. It is weighted at the back so it rests firmly while cycling and its creators say it gives greater cover to the head than traditional helmets.
The Hövding collar's designers wanted to come up with something fashion-conscious cyclists would be happy to wear.
This is not the end of the designers' difficulties – they also have to persuade cyclists to trust that their invention will not let them down. "I think people are very positive towards inventions until they are faced with the opportunity to try it themselves and then they turn into sceptics or they turn scared," said Alstin. "There are always early adopters or people who want to try everything new but the majority of people want to just wait and see how it goes and hear from someone they really trust, someone really close to them that 'yes, it is actually working and saved me in an accident'.
"It takes a lot of time to convince people. In the markets that we have been in the longest, we can definitely see how it is turning and finally people are starting to believe that this is here and now and I can finally trust this product."
With 20 employees at its Malmö headquarters, the company has secured its €13m funding from 10 investors, with Alstin and Haupt retaining a minority shareholding. The company is expected to move into profit in two years, although sales figures remain confidential. The company will only say that the invention is used equally by both sexes.
The arrival of the collar in London bike shops brings the number of stores it is sold in to 300 across 15 countries. Japan and north America beckon for future expansion, said Alstin. But the elaborate design comes at a price – including the fabric shell, which can give it a fashionable look, it costs £299. Additional fabric shells are another £49. Once the airbag itself is inflated in a crash, it cannot be used again.
Alstin admitted the cost was far higher than traditional helmets, which can cost a tenth of the price. "We have lowered the price every time we have had a chance to do that. We are working really hard to do that to reduce costs all the time.
"New products will always be the most expensive in the beginning and of course as volumes go up, there is even more room for price reductions. But I mean of course, compared to a regular helmet, it is way more expensive. For a student or a family with a lot of kids, it is a lot of money and all I can say is that it is a very expensive product to produce so we don't really have the possibility to sell it any lower at this point."
While the Hövding has just arrived in the UK, the airbag has already saved cyclists in other countries from injury, she said. "It is an amazing feeling to see it out on the streets being worn but most motivating of course is when you get the feedback from people who have been in accidents and have been saved," she said.
"Most of our customers are people who have never worn a traditional helmet because they don't like them for different reasons and they are extremely thankful, but they know that if they had been in this accident without Hövding, 'I would have been completely unprotected and I don't know how that would have ended for me'."
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