Exclusively for Prime members, Amazon offers the Amazon Dash Wand with Alexa for $20 with free shipping. Even better, after you register your Dash Wand, you'll receive a $20 Amazon Credit. That essentially makes the Dash Wand free.
The Amazon Dash Wand is a WiFi- and Bluetooth-enabled device that allows you to add items to your cart by either saying or scanning whatever it is you want. The $20 credit will expire on June 18, 2018.