Here's how you can control when Siri listens to you in iOS 7.1 by using the Home button.
1. Press and hold the Home button and state your question or request to Siri.
2. To stop Siri from listening, just release the Home button.
This is a quick and easy way to control Siri's listening in iOS 7.1.
Ever had a time where you're using Siri and your iPhone or iPad doesn't stop listening when you want it to? Maybe someone else is talking or there's noise in the background, but you're done and the wave form just won't stop.More at iMore
Additional resources for iOS