AEDs perform a range of self diagnostic checks on themselves to detect any issues or faults. They check the state of the battery and condition of the battery, it checks the software to ensure everything works as it should, it checks connectivity issues and if all is well it will shut itself down again till the next diagnostic check.
Whichever model of AED you have it will alert you that a self diagnostic check had failed, this could be an audible alarm similar to a smoke alarm when the battery is low, you know that annoying bleep we get in the early hours of the morning. Some will have a flashing light to let you know that the diagnostic check had failed, and some will do both.
Hence AEDs and maintaining them.
So check your AED(s) WEEKLY and document it’s been checked and functioning correctly with no faults, if a fault is detected rectify the fault straight away.