This one time, at math camp, @colinmac10 showed us how to use Socrative for exit tickets (and more!) if most students have a smartphone or laptop with them.
The Exit Ticket option will ask 4 questions. While students answer the first 3, you have time to create a question on the whiteboard. Very little advance prep is required and students can do the entire thing in about 2 min + time to solve the last problem.
Megan Hayes-Golding 
THANK YOU for this video. I will admit I had to watch it about 5 times to get mine to work. My math coach was going to show us how to use this, but our district policy says no electronic devices in the classroom. Our principal may be amenable to using technology in the classroom if there is educational purpose. This would provide great data.
I hope it helps! I know I never could have used this in my old school because the kids were tech abusers (texting during class was so common I had to choose pants with big pockets to hold all the phones I took up each day). However, when the kids are held accountable for their responses AND your administration is onboard, Socrative is a pretty cool tool. Also see PollEverywhere as an alternative, especially if you have a mix of kids with standard mobile phones with texting plans.
Sweet! Thanks for the video! I was just thinking about exit tickets today!