What is a defibrillator?
A defibrillator, also known as an automated external defibrillator (AED), is a life-saving medical device used to treat sudden cardiac arrest. It works by delivering a controlled electric shock to the heart to help restore a normal heart rhythm. Using a defibrillator quickly before paramedics arrive can dramatically improve the chances of survival in those critical first few minutes. Defibrillators are most commonly found in public spaces, schools, community settings and workplaces across the UK.
Browse our comprehensive range of semi and fully automatic defibrillators for schools and workplaces, with additional accessories to help you install and maintain your defibrillator.
When should you use a defibrillator?
Defibrillators are used to treat someone in cardiac arrest, which is when someone’s heart stops beating normally, and they are unresponsive and not breathing.
Why is using a defibrillator important?
A cardiac arrest can happen to anyone. Every year, approximately 55 out of every 100,000 people experience an out-of-hospital cardiac arrest, with most occurring in the home or workplace. In 7 out of 10 cases, CPR is attempted by a bystander, and in less than 1 out of 10 cases, a public access defibrillator is reported as being used.
A bystander performing CPR and using an automated external defibrillator (AED) can increase the chances of survival by two to fourfold.
Information from 2025 Resuscitation Guidelines, Resuscitation Council UK.
What should you consider when buying a defibrillator?
- Who will likely need the defibrillator – in school settings, children will need separate paediatric defibrillation pads
- Storing your defibrillator – fixed-location defibrillators should be stored in a cabinet or wall bracket, with appropriate signage
- Training – although you do not need medical experience to use a defibrillator, AED training can ensure you are familiar with the device and can act quickly in an emergency. Rescuers will still need to perform CPR, so it is important to know how to do this
- Educating your community – ensure your colleagues or community members are aware of the defibrillator, its location, how to access it, and how to use it.
How much is a Defibrillator?
The cost of automated external defibrillators can vary depending on the model and its features. Typically, defibrillators can cost between £800 and £2,500.
All defibrillators we sell:
- come with voice instructions to guide the rescuer through each step of the rescue
- provide a shock to the patient either automatically or at the press of a button
- perform daily, weekly and monthly self-tests to let you know if the device is ready for use.
Defibrillators come with varying degrees of protection from dust and water, making some more suitable in harsher environments than others. Some defibrillators will come with additional features, such as an LCD display screen for visual instructions, real-time CPR feedback to let the rescuer know the quality and effectiveness of their CPR, or an ECG display for more professional models.
To help you decide which defibrillator would best be suited to your workplace, home or community, we have answered some commonly asked questions and showcased a comparison table of our defibrillator range below.
You can also explore our wide selection of semi-automatic and fully automatic defibrillators designed for schools and workplaces, along with essential accessories to support the installation and maintenance of your device.
Popular models
St John Ambulance HEART One Semi-automatic Defibrillator
St John Ambulance HEART Two Semi-automatic Defibrillator
ZOLL AED 3 Fully Automatic Defibrillator
Philips HeartStart HS1 Semi-automatic Defibrillator
Popular models
Her are some of the more popular defibrillator models our customers buy
Shop all defibrillatorsHow much does a Defibrillator cost to maintain?
Defibrillator pads and batteries can cost anything from £20 to £300 to replace depending on the model.
Pads and batteries will need to be replaced when they expire or when the defibrillator pads have been used in a rescue. For more information about defibrillator maintenance, please read our guide for defibrillator maintenance and upkeep.
How much does Defibrillator training cost?
While defibrillators are easy to operate and can be used by anyone without medical experience, training employees in how to use a defibrillator ensures they can act quickly and confidently in an emergency, as they will be familiar with the device.
For more information about our defibrillator and CPR training course and prices, please see our training course page.
Should a Defibrillator be kept in a locked cabinet?
Guidance on locking the cabinet can vary between ambulance trusts. We recommend checking with your local ambulance trust to follow their advice.
Some defibrillator cabinets are also alarmed rather than locked, letting people know that the defibrillator is being accessed.
St John Ambulance believes defibrillators should be made as accessible as possible to ensure they can be accessed quickly in an emergency.
Do Defibrillators need to be registered with the ambulance service?
We've partnered with the British Heart Foundation, Resuscitation Council UK and UK Ambulance Services to make defibrillators more accessible via The Circuit and give them the best chance of saving a life.
Early defibrillation before emergency services arrive can help double a person’s chances of surviving an out-of-hospital cardiac arrest. However, in the UK, defibrillation is received in less than 1 out of 10 cases.
Did you know there are an estimated 100,000 defibrillators in the UK, but only 30% of defibrillators are known to ambulance services? This means that tens of thousands of defibrillators aren't used when needed because emergency services don’t know where they are.
Find out more about The Circuit and answers to frequently asked questions.
Choosing the right defibrillator for the first time can feel overwhelming, but with the right information, it becomes much simpler. Understanding how defibrillators work, where they are used, and what features to look for helps ensure you choose the right option for your environment.
Whether you’re buying a defibrillator for a workplace, school, community space or public venue, selecting an AED defibrillator that is easy to use and properly maintained is essential. As the UK’s leading first aid charity, St John Ambulance provides expert guidance, trusted defibrillators and ongoing support to help you feel confident in your choice.
If you’re ready to buy a defibrillator, you can explore our range of automated external defibrillators or learn more about CPR and defibrillator training to ensure you’re prepared to act in an emergency.
