Although I was booked in sleeper to and from Chicago a month ago, I chose to put my bags in a locker rather than "checked" in the first class lounge. I considered peace of mind for my valuables over price as I walked around downtown Chicago for a couple of hours with a camera taking pictures.
To my dismay, the lockers are only in the baggage-claim area, which is glass-walled on 2 sides with only one door, as I recall.
The real trick, however, was trying to figure out how to make the lockers work! Just figuring out it was necessary to use the computer screen BEFORE selecting a locker and then getting it to function was a real trick in itself! Have a lot of singles handy! It requires an up-front payment of one hours-worth of storage and will collect the rest when you return. Also...it takes your fingerprint so it can verify you really ARE the owner of that locker when it comes time to claim your bags. Remember if you use your right finger or left.
I didn't see the Smarte-Carte employee in the area when I went to store my stuff, but I did see him when I came back about 2 hours later.