If your iPad is plugged into a power source, you don’t have to press and hold the Home button to start Siri.
Simply say, “Hey Siri” and follow up with a request. This is perfect for when your iPad is charging on your desk or nearby and you can’t reach the Home button.
If you don’t have this function enabled yet, you’ll need to teach Siri your voice. Open Settings, select Siri & Search and enable Listen for “Hey Siri”. You’ll be prompted to speak some phrases into the iPad to configure it, and then you’re good to go.