First of all let me thank the whole Duolingo team for a fantastic website and phone app. After using Duolingo for a couple of weeks I have a suggestion which may move it forward. As everyone knows, when you log into the website you are asked if you would like to use a microphone. This is great, as it really helps you get handle on pronunciation. However, the one thing everyone who has the app, has, is a microphone on their smartphone, yet there is no option to use it. Maybe you could look at this and in a future update include it.
Thank you :) We don't have speak challenges in the Android app (yet!). The settings are different for the use of the microphone on the site and the iPhone app. You can have one enabled and the other not depending on your settings.