Plickers lets you poll your class for free, without the need for student devices. Just give each student a card (a "paper clicker"), and use your Android smartphone or tablet to scan paid to do instant checks-for-understanding, exit tickets, and impromptu polls. Best of all, your data is automatically saved, student-by-student, at plickers.com. Happy teaching!
+ Fix for camera permissions issue on newer devices (Android 6.0) + Disabled Android auto-backup, which was causing account issues for some users