NL-Alert
A message on your mobile phone saying what is happening and what to do. It is switched on by default on almost every phone.
Siren
There is a test every first Monday of the month at 12:00. Hear the siren at another time? Go inside, close windows and doors, switch off ventilation and listen to the regional broadcaster.
Emergency broadcaster
If the internet is down, the regional broadcaster on the radio gives reliable information.