An AED (Automated External Defibrillator) is a life-saving device designed to help people experiencing certain serious cardiac emergencies. AEDs are increasingly found in workplaces, schools, sports facilities, shopping centres and public buildings throughout the UK.
This guide explains what an AED is, how it works, when it may be used and how it fits into an emergency response.
This information is general guidance and does not replace professional medical advice or formal first aid training.
AED stands for Automated External Defibrillator.
An AED is a portable electronic device that can analyse a person's heart rhythm and determine whether a controlled electrical shock may be required.
The device provides clear voice instructions and is designed so that members of the public can use it during an emergency.
When someone suffers a sudden cardiac arrest, their heart may stop pumping blood effectively around the body.
Without oxygen-rich blood reaching the brain and vital organs, survival chances can decrease quickly.
Rapid access to CPR and an AED can play an important role in the chain of survival.
See CPR Explained: Adult, Child and Baby CPR.
An AED analyses the casualty's heart rhythm through adhesive pads placed on the chest.
The device then determines whether a shock is appropriate.
If a shock is required, the AED will provide instructions and guide the user through the process.
Modern AEDs are designed to prevent accidental shocks when they are not needed.
| Step | What the AED does |
|---|---|
| 1 | Analyses the heart rhythm |
| 2 | Determines whether a shock is appropriate |
| 3 | Provides spoken instructions |
| 4 | Guides the user through the process |
| 5 | Supports ongoing emergency response |
An AED may be used when a person:
If someone is unresponsive and not breathing normally, call 999 immediately and follow the instructions provided by the emergency operator.
See First Aid for an Unconscious Person.
An AED does not replace CPR.
Both are important parts of an emergency response:
Where available, an AED should be brought to the casualty as quickly as possible while CPR continues.
Yes. Modern AEDs are specifically designed to be used by members of the public.
The devices provide step-by-step voice instructions and are intended to be simple to operate during emergencies.
Although training is beneficial, many people successfully use AEDs with guidance from the device and emergency services.
AEDs can often be found in:
Many communities also maintain publicly accessible defibrillators that can be accessed during emergencies.
If an AED is nearby, the emergency operator may help direct callers to its location.
The operator can also provide instructions regarding CPR and the use of the device while professional help is on the way.
See When to Call 999 vs 111 vs GP.
There is no universal legal requirement for every workplace to have an AED. However, many organisations choose to install them as part of their emergency preparedness arrangements.
Factors that may influence this decision include:
See Workplace First Aid Risk Assessment.
No. AEDs are specifically designed for public use.
No. The device analyses the heart rhythm and only advises a shock when appropriate.
No. CPR and AEDs work together as part of the emergency response.
Modern AEDs provide clear spoken instructions to guide users through each step.
Many people encounter AEDs in public places but are unsure how they work.
Understanding the purpose of AEDs can help people feel more confident responding during an emergency and can support faster action when every minute counts.
See Why Response Time Matters in First Aid.
AEDs are designed to help people experiencing certain life-threatening cardiac emergencies. They are increasingly available throughout the UK and can be used by members of the public.
Combined with rapid emergency calls and CPR, AEDs form an important part of an effective emergency response.
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