Plickers
https://play.google.com/store/apps/details?id=com.plickers.client.android&hl=en

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 them 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. This will be added to Education and Academic Resources Subject Tracer™. This will be added to Artificial Intelligence Resources 2019 Subject Tracer™. This will be added to Business Intelligence Resources Subject Tracer™. This will be added to Entrepreneurial Resources Subject Tracer™. This will be added to the tools section of Research Resources Subject Tracer™.