If you have seen a defibrillator in a workplace, school, sports club or public place, you may have wondered what is an AED, when should it be used and whether an ordinary member of the public can operate one.

An AED, or Automated External Defibrillator, is a portable device used to help someone in cardiac arrest. It analyses the heart’s electrical rhythm and, when appropriate, delivers or advises an electrical shock.

AEDs are designed so that people without medical training can use them. The device provides clear instructions and will only advise a shock when its analysis identifies a shockable heart rhythm.

Rapid recognition of cardiac arrest, calling 999, starting CPR and using an AED as quickly as possible can give someone their best chance of survival.

This guide explains what an AED is, how it works, when to use one, where AEDs should be located and what businesses, schools, community organisations and members of the public should know about defibrillators.

What Is an AED?

AED stands for Automated External Defibrillator.

It is a portable medical device designed to analyse the heart rhythm of someone in cardiac arrest and determine whether defibrillation is required.

The word “automated” does not mean the AED takes control of the entire emergency.

The rescuer still needs to:

recognise that something is seriously wrong
call 999
start CPR
retrieve or send someone for the AED
expose the casualty’s chest
attach the electrode pads
follow the AED’s instructions
continue CPR when instructed

The AED then performs the complicated part: analysing the heart’s electrical rhythm and determining whether a shock is appropriate.

What Is an AED Used For?

An AED is used when someone is in cardiac arrest.

A person in cardiac arrest will be:

unresponsive
not breathing normally

They may occasionally gasp, make unusual breathing movements or initially display seizure-like activity.

These signs should not be mistaken for normal breathing.

Current Resuscitation Council UK guidance emphasises calling 999 as soon as you identify that a person is unresponsive. Assess breathing while waiting for the emergency call to be answered and follow the call handler’s instructions.

If the person is unresponsive and not breathing normally, start CPR and use an AED as soon as one becomes available.

Our step-by-step guide explains how to use an AED during a cardiac arrest.

What Is the Difference Between Cardiac Arrest and a Heart Attack?

These terms are sometimes used as though they mean the same thing, but they do not.

Cardiac arrest

Cardiac arrest occurs when the heart suddenly stops pumping blood effectively around the body.

The casualty becomes unresponsive and stops breathing normally.

This is when CPR and an AED may be required.

Heart attack

A heart attack occurs when the blood supply to part of the heart muscle becomes blocked.

Someone experiencing a heart attack will often still be conscious and breathing.

Symptoms can include:

chest pain or discomfort
pressure, heaviness or tightness in the chest
pain spreading into the arm, jaw, neck, back or stomach
breathlessness
sweating
nausea or vomiting
feeling light-headed or very unwell

A heart attack can lead to cardiac arrest, but the two conditions are not the same.

If someone has symptoms that could indicate a heart attack, call 999.

You do not attach an AED simply because someone reports chest pain. If they become unresponsive and are not breathing normally, however, cardiac arrest should be suspected and the AED should be used.

What Is an AED Actually Doing to the Heart?

The heart has its own electrical system that coordinates its contractions.

During some cardiac arrests, this electrical activity becomes dangerously abnormal and the heart cannot pump blood effectively.

Defibrillation delivers a controlled electrical shock through the chest.

The purpose is not simply to “restart” a heart that has completely stopped.

Instead, a shock can interrupt certain abnormal electrical rhythms, allowing the heart’s normal electrical system an opportunity to regain control.

This is why the AED analyses the rhythm before advising a shock.

Will an AED Always Deliver a Shock?

No.

This is one of the most important things to understand about an AED.

Not every cardiac arrest has a heart rhythm that can be treated with defibrillation.

Once the electrode pads have been attached, the AED analyses the casualty’s heart rhythm.

It will then tell you whether a shock is advised.

If the rhythm is not shockable, the AED will not advise a shock.

The rescuer should continue CPR according to the device and ambulance call handler’s instructions.

This means you do not need to decide whether the casualty needs an electrical shock. The AED makes that assessment.

Can Anyone Use an AED?

Yes.

You do not need to be a doctor, paramedic or trained first aider to use an AED in an emergency.

Modern public-access AEDs are designed to guide rescuers through the process using:

spoken instructions
diagrams
illuminated buttons
visual prompts
screen instructions on some models

Some devices also provide CPR feedback.

If someone is in cardiac arrest and an AED is available, do not wait for a trained person to arrive before using it.

Call 999, start CPR and follow the AED’s instructions.

Do You Need AED Training?

Formal training is not required before someone can use an AED during an emergency.

However, there is an important difference between being allowed to use an AED and feeling confident enough to act quickly.

Practical training allows people to practise:

recognising cardiac arrest
calling for emergency help
chest compressions
rescue breaths
retrieving an AED
preparing the casualty
attaching pads
following the AED prompts
delivering a shock safely
restarting CPR immediately

This familiarity can reduce hesitation during a real emergency.

AED use forms part of our Emergency First Aid at Work and First Aid at Work courses.

What Is an AED Pad?

AED electrode pads are adhesive pads attached to the casualty’s bare chest.

The pads allow the AED to analyse the heart rhythm and, where appropriate, deliver the electrical shock.

For a typical adult, one pad is positioned:

below the right collarbone

and the other:

on the left side of the chest, beneath the armpit

The pads normally contain clear diagrams showing their correct position.

Follow the diagrams on the pads and the AED’s instructions.

Can You Use an AED on a Child?

Yes.

An AED can be used on children and babies in cardiac arrest.

For infants and smaller children, paediatric mode should be used when available.

Depending on the AED model, this may involve:

separate paediatric pads
a child key
a child button
a switch
selecting a paediatric setting

If paediatric capability is unavailable and an AED is the only defibrillator available, do not delay defibrillation.

Our dedicated guide explains how to use an AED on a child or baby, including paediatric modes and pad positioning.

What Is an AED’s Role Alongside CPR?

CPR and defibrillation work together.

CPR helps maintain some circulation of oxygenated blood to vital organs while the heart is not pumping effectively.

An AED may then be able to treat a shockable heart rhythm.

Therefore, finding an AED should not mean abandoning CPR unnecessarily.

If several people are present:

one person can call 999
one can start CPR
another can retrieve the AED

When the AED arrives, apply the pads with as little interruption to CPR as possible.

Stop touching the casualty when the AED tells you it is analysing the rhythm.

If a shock is advised, make sure nobody is touching the casualty.

After the shock, restart CPR immediately when instructed.

What Is the Difference Between a Semi-Automatic and Fully Automatic AED?

AEDs are commonly available in two operating styles.

Semi-automatic AED

A semi-automatic AED analyses the heart rhythm and, if a shock is required, instructs the rescuer to press the shock button.

Fully automatic AED

A fully automatic AED analyses the rhythm and, when a shock is required, delivers it automatically after warning rescuers to stand clear.

Both types are designed for straightforward use.

The most suitable choice may depend on the environment, users, organisational preference and individual AED features.

Our portable AED buying guide explains these differences and the other features worth comparing.

Are All AEDs Portable?

Most AEDs designed for workplaces and public access are portable.

They are commonly stored:

in a carry case
on a wall bracket
inside an indoor cabinet
inside an external AED cabinet

Some are designed with particular environments in mind, including workplaces, sports facilities, community locations and more demanding outdoor environments.

Portability should not be considered in isolation.

When comparing devices, also consider:

weight
durability
IP rating
battery life
electrode pad life
paediatric capability
warranty
operating temperature
storage temperature
replacement consumable costs
CPR feedback
connectivity

Where Should an AED Be Located?

An AED needs to be somewhere people can reach quickly during an emergency.

Good AED positioning should make the device:

easy to see
easy to find
clearly signposted
rapidly accessible
appropriately protected
accessible for as many hours as reasonably possible

For a community AED, 24-hour public access can be particularly valuable.

An AED hidden in an office cupboard may technically be present but can be much less useful during a cardiac arrest.

Our detailed AED placement guidelines explain workplace and community positioning, signage, cabinets and accessibility.

What Is an AED Cabinet For?

AED cabinets help protect and identify defibrillators.

Indoor cabinets can make the device easier to locate and keep equipment together.

External cabinets provide additional environmental protection and may include heating to protect the AED from low temperatures.

For community AEDs, external cabinets can allow the device to remain available even when the host building is closed.

Current Resuscitation Council UK guidance favours unlocked AED cabinets because they avoid unnecessary delay in retrieving the device during an emergency.

What Is The Circuit?

The Circuit is the national defibrillator network.

It connects information about defibrillators with UK ambulance services.

Registering an AED can provide ambulance services with information about:

its location
when it is accessible
whether it is emergency ready
the status of its electrode pads

This can help ambulance services direct members of the public towards available AEDs during a cardiac arrest.

Public and community AEDs should therefore be registered with The Circuit.

You can also use Defib Finder to look for registered defibrillators available nearby.

Are AEDs a Legal Requirement in UK Workplaces?

There is no blanket UK law requiring every workplace to have an AED.

Employers do, however, have duties under the Health and Safety (First-Aid) Regulations 1981 to provide adequate and appropriate first aid equipment, facilities and personnel.

Employers should carry out a first aid needs assessment to determine what provision is appropriate for their workplace.

Factors may include:

workplace hazards
number of employees
workforce profile
shift patterns
remoteness
emergency medical response times
previous incidents
people other than employees who may be present

An AED may form part of that provision.

Our guide to whether AEDs are a legal requirement in UK workplaces looks at employer responsibilities, HSE guidance, PUWER and workplace needs assessments in more detail.

What Is an AED. Automated External Defibrillators Explained

What Is an AED Likely to Cost?

For a typical public-access AED in the UK, a realistic purchase price is often around £800 to £1,500, although specialist devices can cost considerably more.

The AED itself is not the only cost.

You may also need to budget for:

a cabinet
installation
signage
replacement electrode pads
replacement batteries
paediatric accessories where required
rescue accessories

Replacement intervals and prices vary considerably between manufacturers.

This means the cheapest AED to purchase is not necessarily the cheapest to own.

Our guide to AED costs in the UK explains purchase prices and longer-term ownership costs.

Can You Get Funding for an AED?

Sometimes.

Community groups, charities, sports clubs and other organisations may be able to access:

charitable funding
community grants
council funding
sponsorship
fundraising
crowdfunding
national defibrillator programmes

Funding availability and eligibility change over time.

Our guide to AED grants and funding in the UK explains the current options and how to prepare a community defibrillator project.

What Maintenance Does an AED Need?

Modern AEDs generally require relatively little day-to-day maintenance, and most perform automatic self-checks.

However, an AED should never simply be installed and forgotten.

Someone should remain responsible for checking:

the rescue-ready indicator
warning or fault indicators
electrode pad expiry dates
battery condition
physical damage
cabinet condition
accessibility
signage
rescue accessories

The device should also be checked following use.

Our complete AED maintenance guide explains routine checks, batteries, pads, cabinets and what to do after an AED has been used.

Do AED Pads and Batteries Expire?

AED electrode pads have a manufacturer-specified expiry date.

They are also normally replaced after use because they are single-use consumables.

Batteries also have a finite lifespan.

However, there is no single replacement interval that applies to every AED.

Battery and pad lifespan depends on the manufacturer and model.

When purchasing an AED, check:

pad shelf life
battery standby life
replacement cost
availability of replacements
whether paediatric consumables are separate

These factors can make a substantial difference to the lifetime cost of the device.

What Is an AED Readiness Check?

A readiness check is a simple inspection to confirm that the AED appears available for emergency use.

Depending on the device and environment, this may include checking:

the AED is in its correct location
it is accessible
the ready indicator shows normal status
no warning light or alarm is present
the pads are connected where required
pads are within their expiry date
the battery is serviceable
the device has not been damaged
the cabinet is in good condition
rescue accessories are present

Always follow the manufacturer’s instructions for your specific AED.

What Happens After an AED Has Been Used?

After an AED has been used in an emergency, it needs to be prepared for future use.

This will normally involve:

replacing used electrode pads
checking battery status
cleaning the device according to manufacturer instructions
replacing used rescue accessories
checking the carry case
confirming the AED passes its self-test
updating its status on The Circuit where appropriate

Some devices may store information relating to the cardiac arrest that can be accessed by healthcare professionals.

Follow the manufacturer’s post-use instructions.

What Is an AED’s Role in Schools?

AEDs can form an important part of emergency preparedness in schools and colleges.

They are not only there for pupils.

A cardiac arrest could affect:

staff
parents
visitors
contractors
spectators
community users
pupils

Schools should understand where their AED is located, who can access it and whether it has appropriate paediatric capability.

Our dedicated AEDs in schools guide explains school AED provision, child use, positioning, maintenance and emergency preparedness.

What About an AED for Home Use?

Individuals can purchase an AED for their home.

There is no requirement to be a healthcare professional to own one.

Some people may consider a home AED because:

a household member has a known cardiac condition
they live in a remote area
public AED provision nearby is limited
they want additional emergency preparedness

However, owning an AED does not replace calling 999, performing CPR or obtaining professional medical care.

Someone considering a home AED because of an individual’s medical condition should discuss their concerns with an appropriate healthcare professional.

Our guide to AEDs for home use explains the considerations in more detail.

How Effective Are AEDs?

The effectiveness of defibrillation is strongly influenced by how quickly cardiac arrest is recognised and treatment begins.

This is why the chain of survival focuses on:

early recognition and calling for help
early CPR
early defibrillation
effective post-resuscitation care

An AED sitting unused several minutes away is less useful than one that can be located and brought to the casualty quickly.

Likewise, having an AED nearby does not remove the need for immediate CPR.

Our article on AED usage statistics in the UK explores the evidence and explains why early defibrillation matters.

What Should You Look for When Buying an AED?

If you are responsible for purchasing a defibrillator, avoid choosing solely on price.

Compare:

ease of operation
semi-automatic or fully automatic operation
adult and paediatric capability
electrode pad lifespan
battery lifespan
replacement costs
IP rating
CPR feedback
screen or visual prompts
operating temperature
storage requirements
warranty
manufacturer support
availability of consumables

Think about where the AED will be used and who is likely to use it.

A device suitable for a warm indoor office may not necessarily be the best option for an exposed sports or community environment.

Our portable AED guide provides a more detailed buying checklist.

If you are ready to compare equipment, you can also view the current defibrillator range available from Jax First Aid.

Affiliate disclosure: If you purchase through the Jax First Aid link above, First Aid and Safety Training may receive a commission. This does not increase the price you pay.

What Is an AED? The Key Points to Remember

If you want a simple answer to what is an AED, remember these points:

AED stands for Automated External Defibrillator.
It is used when someone is in cardiac arrest.
A person in cardiac arrest is unresponsive and not breathing normally.
Call 999 as soon as you identify that someone is unresponsive.
Start CPR when cardiac arrest is identified.
Use an AED as soon as it is available.
Anyone can use an AED.
You do not need formal AED certification to use one in an emergency.
The AED analyses the casualty’s heart rhythm.
It will only advise or deliver a shock when appropriate.
AEDs can be used on children and babies.
CPR should continue with interruptions kept as short as possible.
AEDs need appropriate positioning, checking and maintenance.
Public-access AEDs should be registered with The Circuit.
Practical training can make people much more confident about acting in a real emergency.

Learn CPR and AED Skills Before You Need Them

Understanding what is an AED is useful, but practical experience can make the equipment far less intimidating.

During first aid training, learners can actually handle an AED trainer, attach electrode pads to a manikin, follow the prompts, practise CPR and experience the sequence they would follow during a cardiac arrest.

First Aid and Safety Training provides practical CPR and AED training as part of our regulated first aid qualifications.

You can explore our Emergency First Aid at Work course, First Aid at Work course or find out about first aid training across the North East.

For training at your organisation, contact First Aid and Safety Training and we can discuss the most appropriate option.

You can also see our South Shields training location and customer reviews on Google Maps.

Real Skills, Real Confidence.