You can see the lock history if you are the Owner or an Admin for that lock. Both the mobile app and web portal contain a history that details when and by which eKey the Kevo is locked/unlocked. Go to My Locks & eKeys, select the lock and choose the history icon at the bottom of the screen.
Go to My Locks & eKeys > (select a lock) > History icon (second tab from the right on the bottom of the screen)
From your My Kevo homepage, click on the "History" icon (on the top bar, second from the right)