Amazon wants you to join Prime... but that's not all it wants

'Prime' time for Amazon?

Amazon's Prime Day sales event is as much a vehicle for encouraging shoppers to sign up for a $99 annual Prime membership as it is about juicing its summer sales. But that's not all the online retailer is angling to accomplish on the self-invented sales holiday, which falls on July 12 this year.

In addition to offering discounts for new and existing Prime members, Amazon on Friday said these shoppers can use Alexa, its cloud-based voice service, to receive additional discounts and exclusive deals. To do so, they need to already own or buy an Amazon Echo, Echo Dot or Amazon Tap speaker system, which typically cost between $90 and $180. (The Dot was listed as "Sold Out" on Friday.)

The company is also using Prime Day as a means to upsell consumers on its Prime Now service, which for $7.99 promises one-hour delivery on qualifying items in certain cities. (Two-hour delivery is free). It's doing so by giving shoppers $10 off their first Prime Now order, along with a discount code for another $10 off a Prime Now purchase later in the month.

And to encourage shoppers to sign up for an Amazon Prime Store Card, a credit card that gives members 5 percent back on Amazon purchases, it is offering a $50 Amazon gift card.

All of these strategies give non-members additional reasons to consider Prime, beyond free two-day shipping. They also encourage Prime members to make more purchases through Amazon, whether for convenience or pricing purposes. By owning an Alexa-enabled device, shoppers can order items from the retailer by speaking a voice command. And holders of an Amazon card would be more likely to order additional paper towel rolls from its site if it meant they'd receive a kickback.

As the program matures and membership growth slows in the U.S., Amazon will rely more heavily on getting members to stick with and spend more with the service.

"Many see free two-day shipping as the primary reason customers try Amazon Prime, [but] enhanced streaming video and other offerings provide added incentive for members to continue to renew," Mike Levin, co-founder of Consumer Intelligence Research Partners, said earlier this year.