More than 8 million shoppers in the U.S. are hearing an echo in their homes—an Amazon.com Inc. Echo, that is.

Data from securities research firm Consumer Intelligence Research Partners LLC, or CIRP, shows that 8.2 million U.S. shoppers own one of the voice-activated digital assistant devices. That’s up 173% from an estimated 3 million shoppers this time last year. CIRP estimates that Amazon sold 3.1 million devices in the fourth quarter of 2016 alone, up from 1 million devices sold during the same period last year. CIRP’s data is based on a survey of 500 shoppers in the U.S. who bought at least once on Amazon during the fourth quarter ended Dec. 31.

Amazon in December reported that sales of Echo devices increased ninefold during the holidays compared with the same period in 2015. Amazon, No. 1 in the Internet Retailer 2016 Top 500 Guide, could not be reached for additional comment.

“The installed base of homes with Amazon Echo devices has grown dramatically, and close to tripled in the past 12 months,” said Mike Levin, partner and co-Founder of CIRP. “Amazon promoted Echo aggressively over the holiday shopping season, with especially aggressive pricing for the Echo Dot. The new models account for close to half of (Echo) sales since Amazon introduced them earlier in 2016.” Amazon rolled out the portable Amazon Tap and hockey puck-size Echo Dot devices in March.

Amazon also promoted the Echo devices—powered by Alexa, Amazon’s voice-activated digital assistant—in the runup to Prime Day. Amazon held its second annual 24-hour Prime Day sales event on July 12 for customers who pay $99 a year to access such Prime services as expedited shipping, streaming video and photo storage. Amazon offered Prime customers $10 off their first voice-based purchase of $20 or more in early July, and then rolled out a handful of daily deals available only when ordered by voice through Alexa.

Not only are more shoppers buying Echo, more shoppers are aware of the devices. 82% of all Amazon shoppers in the U.S. are familiar with the Echo, nearly double the 47% of shoppers who knew about the devices a year ago.