Be prepared for the test of an alert system which will be sent to all mobile devices in Australia on Monday afternoon.

AusAlert is an emergency warning system designed to send alerts directly to compatible mobile devices during disasters, to help keep Australian communities informed, and protecting lives and property.

Monday's AusAlert test will take place at 2pm AEST, and will be sent to most phones, and some smart watches and tablets.

At the time of the test, a single Critical AusAlert test will be sent, with a message clearly stating it is a test.

Devices will vibrate and play a siren-like warning sound for about 10 seconds.

There is no need to do anything at the time of Monday's alert, as it is just a test.

However, in an actual disaster, an AusAlert will likely tell recipients about the type of emergency; where it is located; how serious it is; what to do; the name of the emergency organisation that has sent the AusAlert; and where to find more information.

Devices which don't receive a test alert may be older and may not support AusAlert, meaning they are not compatible; may not be updated to a software version that allows emergency alerts to be received; or might not have mobile signal at the time of the test.

This is all okay, as finding out how devices behave is one of the reasons the system is being tested.

The alert cannot be turned off via device settings, so the only way not to receive a critical alert is to turn your mobile device off or switch it to aeroplane mode.

If receiving an AusAlert test message will disrupt you or cause you or someone you know to feel unsafe, mobile devices should be switched off or to aeroplane mode before the scheduled time, and left off for at least one hour.