Hello Frank,
below are the events and alarms when the WLC is failover.
Severity,"Created On","Name","Event","Created By","Cleared On","Cleared By","Event Type","Event Precedence","Model Type Name"
Major,"Mar 3, 2016 3:25:05 PM SGT","xxxxxxx","This notification is generated when Secondary WLC has switched the state to active.","System","Mar 10, 2016 11:31:33 AM SGT","xxxx","0x6760012","10","GnCiscoDev"
Critical,"Mar 10, 2016 5:50:47 PM SGT","xxxxxxx","Device xxxxxxx of type GnCiscoDev has stopped responding to polls and/or external requests. An alarm will be generated.","System","Mar 10, 2016 5:51:33 PM SGT","System","0x10d35","10","GnCiscoDev"
,"Mar 10, 2016 5:51:33 PM SGT","xxxxxxx","Model xxxxxxx of type GnCiscoDev has been contacted.","System","","","0x10301","10","GnCiscoDev"
,"Mar 10, 2016 5:51:33 PM SGT","xxxxxxx","The condition causing the loss of contact on the device model has cleared ( name - xxxxxxx, type - GnCiscoDev ).","System","","","0x10d30","10","GnCiscoDev"
,"Mar 10, 2016 5:50:47 PM SGT","xxxxxxx","Contact has been lost with model xxxxxxx of type GnCiscoDev.","System","","","0x10302","10","GnCiscoDev"