WAS siren — what to do when the alarm sounds
Machine translation from Dutch, not yet checked by a clinician.
The WAS siren (the Dutch national warning system) sounds when there is a serious threat. Know how to tell the monthly test from a real alert, and what to do immediately.
What to do
• Go indoors immediately — a solid building offers protection
• Close all windows, doors and ventilation openings
• Switch off mechanical ventilation (heat recovery units, extractor fans)
• Tune in to NPO Radio 1 (93.4 FM) for official instructions
• Check NL-Alert on your phone
• Stay inside until the all-clear sounds (a steady, continuous tone)
Do not do
• Do NOT go outside to see what is happening
• Do NOT call 112 for information — keep the line free for emergencies
• NEVER ignore a siren outside the first Monday of the month
• If there is a chemical smell or visible smoke: do NOT go to the cellar — gas clouds sink
Warning signs
• Burning eyes, throat irritation or dizziness — go to a higher floor or leave the building on the sheltered side
• Smoke or flames in the building — evacuate by the stairs
Get help if
• Someone has become unwell from inhaling smoke or chemicals
• You cannot safely reach or leave the building
Why this matters
The monthly test always takes place on the first Monday of the month at 12:00. Any other time is a real alert. Acting fast and correctly limits exposure to dangerous substances or other threats.
Source: Rijksoverheid Crisisbeheersing; Gemeente Amsterdam · reviewed 2025-01-01