How to Choose a Defibrillator (AED): Semi-Auto vs Fully Automatic Compared

The best defibrillator for your workplace, school, or sports club depends on three things: whether you want a fully automatic or semi-automatic unit, the level of CPR coaching built in, and your ongoing budget for pads and batteries. In this guide, we compare the leading AEDs available in the UK, break down the real differences between semi-auto and fully automatic models, and help you pick the right one for your setting.

In this guide

• What is a defibrillator (AED) and how does it work?
• Do I need a semi-automatic or fully automatic AED?
• What features should I look for in a workplace defibrillator?
• AED comparison: how do the top models stack up?
• Are defibrillators required by law in the UK?
• What are the ongoing costs of owning an AED?
• Frequently asked questions

What is a defibrillator (AED) and how does it work?

An Automated External Defibrillator (AED) is a portable device that analyses the heart's rhythm and delivers an electrical shock to restore a normal heartbeat during sudden cardiac arrest (SCA). Every minute without defibrillation reduces the chance of survival by roughly 10%, so having an AED on site can genuinely be the difference between life and death.

Modern AEDs are designed for use by anyone, not just medical professionals. When you open the device and attach the electrode pads to the patient's bare chest, the AED automatically analyses the heart rhythm. It will only deliver a shock if one is needed, so there is no risk of shocking someone who does not require it. Voice prompts and, on some models, an on-screen display guide you through every step.

Do I need a semi-automatic or fully automatic AED?

This is the most common question buyers ask, and the answer depends on who is likely to use the device.

A semi-automatic AED analyses the heart rhythm and tells the rescuer to press a flashing shock button when a shock is advised. This gives trained first aiders a moment of control and confirmation before the shock is delivered.

A fully automatic AED analyses the rhythm and delivers the shock itself after a countdown, with no button press required. This is ideal for settings where the rescuer may have no training at all, such as schools, public spaces, or small offices without dedicated first aiders.

Both types are equally safe. The AED will never deliver a shock unless a shockable rhythm is detected. For most workplaces, the choice comes down to confidence: if your staff have first aid training, semi-automatic is fine. If not, fully automatic removes the hesitation barrier entirely.

What features should I look for in a workplace defibrillator?

Beyond the semi-auto vs fully automatic choice, these are the features worth paying attention to:

• CPR coaching and feedback: Some AEDs measure chest compression depth and rate through the electrode pads, giving real-time voice feedback like "push harder" or "good compressions." This significantly improves CPR quality, especially for untrained rescuers. The HeartSine PAD 500P and Mindray BeneHeart C2 both offer this.
• IP rating (dust and water resistance): An IP55 or IP56 rating means the unit can handle dust and water jets, making it suitable for outdoor cabinets, sports grounds, and construction sites. Most modern AEDs meet this standard.
• Paediatric capability: If children may be present (schools, sports clubs, leisure centres), you need an AED that can switch to a lower energy dose. Some models use separate child pads, while others have a simple switch or key.
• Screen display: Entry-level AEDs use voice prompts and LED indicators only. Mid-range and premium models add an LCD or TFT screen showing visual instructions, an ECG trace, or CPR coaching graphics. A screen is not essential for effective use but can boost rescuer confidence.
• Battery and pad shelf life: These are your main ongoing costs. Look for long-life consumables: most batteries last 4 to 5 years, and pads last 2 to 3 years. Check replacement costs before buying.
• Self-testing: All modern AEDs run daily, weekly, or monthly self-checks and alert you if something needs attention. Some offer Wi-Fi or app connectivity to notify you remotely.

AED comparison: how do the top models stack up?

This table compares the key specifications across four of the most popular AEDs in the Vena Cava range, from budget to premium.

Are defibrillators required by law in the UK?

There is no blanket legal requirement for UK workplaces to have an AED on site. However, under the Health and Safety at Work Act 1974 and the Health and Safety (First Aid) Regulations 1981, employers must provide adequate first aid equipment based on a risk assessment. The HSE strongly recommends AEDs for higher-risk settings and workplaces where emergency services response times are long.

Since June 2023, all state-funded schools in England are required to have at least one AED on their premises, following the Department for Education's statutory guidance. This applies to academies, free schools, and local authority-maintained schools.

Beyond legal requirements, AEDs are increasingly expected in gyms, leisure centres, sports stadiums, shopping centres, train stations, and large offices. Many insurers now offer reduced premiums for sites with registered AEDs, and placing one on The Circuit (the national AED registry) makes it available to ambulance services during nearby emergencies.

What are the ongoing costs of owning an AED?

The purchase price is only part of the total cost of ownership. Here is what to budget for:

• Replacement pads: Electrode pads typically expire after 2 to 3 years (or immediately after use). Expect to pay £40 to £100 per set depending on the model. Some AEDs use combined adult/child pads, saving you from stocking two sets.
• Replacement battery: Most AED batteries last 4 to 5 years in standby mode (some, like the ViVest Power Beat X1, last up to 8 years). Replacement batteries range from £100 to £260.
• Storage: An indoor wall bracket costs £30 to £60. An outdoor heated cabinet with alarm costs £200 to £500. Alarmed cabinets deter theft and alert bystanders when the AED is removed.
• Training (optional but recommended): A half-day AED awareness course typically costs £40 to £80 per person. While AEDs are designed for untrained use, trained staff respond faster and more confidently.

Frequently asked questions

Can I use an AED without any training?

Yes. AEDs are specifically designed for use by untrained bystanders. The device provides step-by-step voice prompts and will only deliver a shock when the heart rhythm requires one. You cannot accidentally harm someone with an AED. That said, a short awareness session (even a 30-minute online course) will help you respond faster and more confidently in a real emergency.

How often do AED pads and batteries need replacing?

Electrode pads typically last 2 to 3 years from the date of manufacture (check the expiry date printed on the packaging). Batteries last 4 to 5 years on average, though some models advertise up to 8 years. Pads must also be replaced immediately after any use, even if no shock was delivered. Set a calendar reminder 3 months before each expiry date so you have time to order replacements.

What is the difference between monophasic and biphasic defibrillation?

All modern AEDs use biphasic technology, which delivers the electrical current in two directions. This is more effective at restoring normal heart rhythm while using less energy, resulting in less damage to the heart muscle. Older monophasic devices (one-direction current) are no longer manufactured. Every AED in the Vena Cava range uses biphasic waveform technology.

Should I register my AED with The Circuit?

Absolutely. The Circuit is the UK's national defibrillator network, managed by the British Heart Foundation. When you register your AED, ambulance services can direct 999 callers to the nearest available device. Registration is free, takes a few minutes, and could help save a life in your area even when the emergency is not on your premises.

Can children use or be treated with an AED?

AEDs can be used on children and infants. For children under 8 years old (or under 25kg), use paediatric pads or switch the device to child mode if available. Paediatric pads deliver a lower energy dose appropriate for smaller bodies. If paediatric pads are not available, adult pads should still be used in a cardiac emergency, as any defibrillation is better than none.