Highly targetted ads are not my concern here, they may even be welcome.

Using heartrate, activity levels, mobilty can probably infer a broad picture of someones health, which of course, would be very valuable to health insurance/life assurance companies.

With this level of privatised surveilance, I'll stick with my mechanical automatic watch thanks.

With sufficient data you could find out much more than that. Your heart rate dropped around 8:20 and spiked shortly after at 8:25? The same happened to 3 million other customers, looks like you are also enjoying the Game of Thrones premiere on HBO.

Located in Hong Kong, elevated heart rate in the evening, spikes match tweets about police activity against protesters? Be prepared to be visited by the authorities.

does google sell data or attention? the whole point of google/facebook ad networks is that THEY keep the data hidden and let you use it as a filter, without being able to see it. they would lose their value if their data was for sale.

google would sell "attention time to people whos heart rate spiked during the world series" but not tell the customers who those people were. you would be outing yourself if you click the ad.

Yes hiring personal trainer ads is the market Google was so desperately after all these years

Global health club market is 87 billion based on, err, googling. How much would that market benefit from highly targeted advertising? Only Google knows that: but you can take a guess from the money they paid for Fitbit. Someone needs to stop them because they can sell any business that benefits from target advertising better than its current owners. The purchase itself is Monopoly abuse.