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BT Red Phone Box defibrillator
The defibrillator machines are secured within high-visibility, vandal-resistant, heated steel cabinets and require a combination code to be opened - available from the emergency services by dialling 999.
The machine talks the user through administering treatment to a casualty, including - if required - delivering a controlled electric shock to restore normal heartbeat.
Up to 200,000 people in the UK suffer a sudden cardiac attack every year, according to BT. Use of defibrillation and cardiopulmonary resuscitation (CPR) increases the chance of survival from five per cent with CPR alone to up to 50 per cent with CPR and a defibrillator.