Emphasize to students your expectations about academic integrity related to the use of clickers or Poll Everywhere
Clearly define these expectations in class and in your syllabus
Consider using time limits for your questions to reduce the chances that a student has time to use another student’s clicker or contact a friend who is not in class with the question and/or answer
Ask a question that can only be answered correctly if the student is in class (what color shirt is a particular TA wearing?)