iPhone users can now access Amazon’s Alexa on the go | Ars Technica

Check this Amazon page for details

"Although this puts Alexa in direct competition with Siri, Apple's voice assistant has the upper-hand in that it's truly hands-free. With Siri enabled, you can say "Hey Siri!" and your iOS device will hear you and listen to your command. To talk to Alexa, you need to open the Amazon Shopping app and press the microphone icon before you can say any commands.

However, Alexa may truly challenge Siri when it comes to smart home controls. You can control HomeKit-compatible devices with Siri in the same way that you can control Alexa-compatible devices with Amazon's assistant. Amazon has a larger library of Alexa-ready smart-home products, and iOS users who already use Alexa to control most of their smart home may embrace this mobile way of doing so. That could also compel users just getting into the smart-home space to buy Alexa-compatible products over HomeKit-ready devices (but there is overlap between those two device groups, too)."

iPhone users can now access Amazon’s Alexa on the go | Ars Technica