Do you have students who constantly want to leave class? Do you want to entice them to stay? Then try bathroom passes. I give my students a sheet of four per semester (each worth 5 extra credit points). If students need to leave class to use restroom, get water, go to get something they forgot, then they need to use a pass and forfeit some extra credit points at the end of the semester. Once they are used up, they are not allowed to leave class. This really makes student question how badly they need to go and will often stop those who just want to get out for no real reason.
These passes allow you to track all necessary information- where they are planning to go, when they left, and when they returned. I usually file mine by class and then if there is ever an issue, I can quickly refer back to it.