Amazon wants to do what it does best, selling subscriptions with a competition-beating value prop. This time around, it hopes to provide a subscription music streaming service for $4 or $5 per month, with the catch being that only Amazon Echo owners would be able to use it, according to a new report from Recode. A cut-rate rival to Spotify, Apple Music et al. might be an interesting offer for Amazon to field, even if it is locked to a certain subset of hardware.

Prime subscribers know that Amazon already offers a streaming music service with a fairly extensive catalogue available on Echo speakers. The Prime Music offering means that members of Amazon’s annual subscription shipping and perks package can basically ask Alexa to play whatever artist they like and Echo will deliver right away. Its main limitation is that it doesn’t offer anywhere near as extensive a catalog as the competition, which is something the new service would look to correct.

This new offering would be similar, delivering ad-free music and full access to a wide catalogue, but would work only on Echo – without web or even smartphone app access. Which is a bold move, because mobile tends to be the keystone platform for most streaming music services.

Echo’s hardware future is also a mystery, however. Amazon is clearly trying to spread the core Echo home speaker far and wide, and also seems to be keen on selling more Amazon Tap Bluetooth speakers. It has discontinued the Amazon Echo Dot, which turned your home theater system into an Echo complete with Alexa voice commands, after a very limited pilot run.

Recode’s report suggests only Echo hardware would get access, but if the streaming service was tied to Alexa and came to third-party devices using its SDK, that might be one interesting way for it to expand. But even as a selling point solely for Amazon-created Echo devices, it could be an interesting way to broaden the appeal of the smart speaker and Amazon’s smart home play in general.