Wayne,

I am with CG4 Asset Tracking and we provide off-the-shelf software that will do the check in/check out functionality.   You probably have something in place by now, but I wanted to shamelessly plug CG4 Asset Tracking.   We have been doing this for over 14 years.   We have been supporting ServiceNow customers for almost two years now.   Our integration is certified with ServiceNow: ServiceNow Share   We have a lot of other functionality that may help you.   Our website is https://cg4assettracking.com or feel free to contact me.