Amazon has a new fitness tracker and wants to get personal

Amazon, the company that made shopping from a La-Z-Boy possible, is going into the fitness-tracking business.

The company started selling a wrist band Thursday that tracks workouts, sleep and body fat. It can also listen to your voice all day and tell you when you sounded happy or sad.

Amazon might already know what books you like and how often you need toilet paper, but the fitness tracker is sure to give the company a wealth of new information about its customers.

Jon Reily, global chief strategy officer at Dentsu Commerce and a former Amazon executive, says that the microphones in the tracker could help it listen to how people talk, which could make its voice assistant Alexa smarter by detecting moods and providing better responses.

And by knowing your body type, Amazon may be able to sell you better fitting clothing, making it less likely that you'll return them, Reily said.

Amazon is asking users to get personal, scanning their body with their smartphone cameras while wearing boxers or a sports bra with bike shorts.

Data has been a concern with other fitness trackers, including FitBit, which tech giant Google is in the process of buying. Regulators in Europe are investigating how the deal could give Google more data to use for personalized ads, furthering its dominate position in the online ad market.

Amazon said health data is encrypted so others can't see, and users can turn off the microphone if they wish.

The fitness tracker, called Amazon Halo, costs $100 and has no screen. There's also a monthly $4 charge to use all of its features. Those who don't pay up can still track steps, sleep times and heart rates.

Seattle-based Amazon has been trying to score a hit in the competitive wearable tech business, which is dominated in the U.S. by FitBit and the Apple Watch. Last year, Amazon started selling wireless earbuds, finger rings and prescription eyeglasses with Alexa built in, but none have proven to be hits so far.