Shares in fitness tracking technology maker Fitbit opened 55 per cent higher at $30.40 as it launched its initial public offering today.
The company made its debut on the New York Stock Exchange this morning at $20 per share under the ticket FIT, raising $732m. It is now valued at more than $4.1bn.
You can see why investors are interested: in 2014 it posted revenues of $745.4m (£469m), and in the first quarter of this year made $337m. Earlier this year it said it has an 85 per cent share of the US wearables market - even President Obama has been photographed sporting one.
However, things haven't gone completely smoothly in the run-up to the IPO: in May, rival Jawbone filed a lawsuit against it, alleging it had stolen information by poaching staff. It also faces rivalry from the Apple Watch, which launched earlier this year.