Using Siri

iphone 6s and newer support "hey Siri"

Ask Siri on iPhone - Apple Support

It is easy. You can enable 'Hey Siri.' After that, you do not need to press the Side button (on iPhone with Face ID) or the Home button on other iPhone models.

Hey Siri is available on iPhone 6s and later. But if you have an iPhone 6 or earlier, Hey Siri will only work when the iPhone is connected to power (that is charging). But since you said 'Side button,' it means your iPhone has Face ID, and it supports Hey Siri.

To enable Hey Siri:

1. Open iPhone Settings.
2. Tap Siri & Search.
3. Enable the switch for Listen for "Hey Siri."
4. Follow the on-screen instructions.

Now, you can summon Siri without pressing any button. Just start your command by 'Hey Siri.' For example, 'Hey Siri, what is the battery percentage.'

:)

Set up and use “hey Siri”.