There is no denying that Amazon's Echo devices and Alexa voice assistant are a huge success at this point. What started out as a weird little cylinder you can command to play music and ask a few questions has now become an entire line-up of devices, an ecosystem that has engendered many integrations from thousands of companies worldwide, and has kickstarted an entire product category and tech section that was nearly non-existent before it.
But since Amazon doesn't divulge any sales numbers for Echo devices, all we've had to go with are estimates from statistics companies or vague numbers from Amazon itself. For example, many reports had stated something along the lines of 8-10 million Echo devices were sold in 2016. Then there's all of 2017 to account for, which depending on whom you believe could go anywhere from 20 to 28 million. But all we know for certain is that Amazon stated it sold millions of Alexa devices just during the Black Friday/Cyber Monday weekend.
For a more tangible number, here's the Play Store install count of the Amazon Alexa app: it just reached 10 million. According to AppBrain it took from November 2014 until May 2017 to reach 5M and then it doubled that in just 7 months now. That means that 10 million users have downloaded the Amazon app on Android. These 10M could own more than 1 Echo, or maybe some of them could own 0 Echos and have downloaded the app to join an existing device set by someone else to sync their contacts and teach their voice. There's also all the iOS users to account for, and then those who might have gotten an Echo and shipped it to a country where the Alexa app isn't officially available and thus had to grab the APK from another source. Yeah... all in all, I tricked you and this number doesn't clarify anything really regarding sales of Echo devices, but it's fun to celebrate milestones especially now as the whole year is drawing to a close.
So congrats on your 10 millionth install, Alexa, and here's to 50 millions and beyond! Google Home already reached that, but we all know it's because of all the Chromecasts.