PWR relates to a loss of power to all or part of the system, this could be due to the main supply failing or an individual unit within the system.
Has the system power recently been interrupted or disconnected in anyway?
Check the supply to the switch.
The iSDX continually carries out internal checks and will reset the alarm in most cases when the problem is resolved. If the supply has failed arrange reconnection, if your supply is OK, report it as a fault for further diagnostics.