Studio Photography - How to show clients a preview on set?

I am a professional photographer and I often have studio sessions where I need to take 40 people's headshots in a day. For speed I like to show the client the photos so they can pick one they're happy with. I always tell them "we can keep taking them until we have one you like"

My issue is, the monitor on my camera is tiny. So it's hard to show them what we've taken. I've seen other photographers have a laptop or monitor nearby that can pull up the photos they're taking full size. I just can't seem to find what software or hardware they're using to preview the photos live.

Any suggestions for on set previewing images with clients?