Whoop’s new wearable can go on your wrist—or in your clothes

Ask people if they’ve heard of the Whoop activity-tracking wearable and they’ll either look at you blankly or say they couldn’t work out, sleep, or live without it. It’s a wrist wearable aimed at fitness fanatics—pro and college athletes, CrossFitters and weekend warriors—and it stands out for a couple of reasons. For one, the only way to get a Whoop wearable is to pay a monthly or annual subscription fee. And two, one of its marquee features is that it tells wearers how much physical strain they can handle on any given day.

You might not think that business model would be worth $3.6 billion. But some investors—and an undisclosed number of subscribers—seem to think Whoop is a big whoop. Now, the Boston company is expanding its product line and getting into “smart” clothing: The Whoop module that’s normally worn on the wrist has been redesigned so that it can also be attached to Whoop-branded athletic apparel. The new Whoop, which the company has dubbed Whoop 4.0, is also the first consumer product on the market to ship with a new kind of super-charged silicon lithium battery.