Emergency vehicle equipment

Emergency vehicle equipment is any equipment fitted to, or carried by, an emergency vehicle, other than the equipment that a standard non-emergency vehicle is fitted with (such as headlights, steering wheels, and windshield/windscreens).
Visual warning devices.
Emergency vehicles of any kind (fire truck, ambulance, police car) are highly likely to be involved in hazardous situations, including relatively common incidents such as a road traffic collision. They are also required to gain access to incidents as quickly as possible, and in many countries, are given dispensation from obeying certain traffic laws; for instance, they may be able to treat a red traffic light or stop sign as a "give way", or be permitted to break the speed limit. However, emergency vehicles usually are not able to treat a railroad crossing as a "give way," because a train cannot be warned in time to stop before the crossing to let the vehicle through. Hence, one of the few things emergency vehicles must yield to are heavy freight and passenger trains. 
For these reasons, emergency vehicles in many countries worldwide, are fitted with visual warnings to alert members of the public (and in particular, other motorists and road users), either as they approach the vehicle, or it approaches them. Visual warnings can be of two types - passive warning or active warning.
Passive visual warnings.
The passive visual warnings are usually inherently linked to the design of the vehicle, and involve the use of high contrast patterns. Older vehicles (and those in developing countries) are more likely to have their pattern painted on, whereas modern vehicles generally carry the retro-reflective designs which reflect light from car headlights or torches (and was invented by 3M). Popular patterns include 'checker board' (alternate coloured squares, sometimes called 'Battenburg markings'), chevrons (arrowheads - often pointed towards the front of the vehicle if on the side, or pointing vertically upwards on the rear) or stripes (along the side - these were the first type or retro-reflective device introduced, as the original 3M reflective material only came in tape form). In some countries, in addition to retro-reflective markings, the vehicles are now painted in a bright yellow or orange colour underneath, in order to maximise visual impact.
Another passive marking form is the name of the emergency service spelled out in reverse on the front of the vehicle (e.g. Ambulance or Fire). This enables drivers of other vehicles to more easily identify an approaching emergency vehicle in their rear view mirrors. The vehicle may also display the name of their owner or operator, and a telephone number which may be used to summon the vehicle.
Ambulances may also carry an emblem (either as part of the passive warning markings or not). Some ambulances may display a Red Cross, Red Crescent or Red Diamond (collective known as the Protective Symbols). These are symbols laid down by the Geneva Conventions, and all countries signatory to it agree to restrict their use to either (1) Military Ambulances or (2) the national Red Cross or Red Crescent society. Use by any other person, organisation or agency is in breach of international law. The protective symbols are designed to indicate to all people (especially combatants in the case of war) that the vehicle is neutral and is not to be fired upon (see Military ambulances), hence giving protection to the medics and their casualties, although this has not always been adhered to.
Many ambulances use the Star of Life, which indicates that the vehicle's operators can render their given level of care represented on the six pointed star.
Active visual warnings.
The active visual warnings are usually in the form of flashing coloured lights (also known as 'beacons' or 'lightbars'). These flash in order to attract the attention of other road users as the emergency vehicle approaches, or to provide warning to motorists approaching a stopped vehicle in a dangerous position on the road (and if the emergency vehicle positions itself to deliberately move people away from an incident, this is called fend off). Common colours for emergency vehicle warning beacons are blue and red, and this varies by country (and sometimes by operator).
The lights can be made to flash via a range of techniques, dependent on the technology used, and the desired end effect. Types of beacon include:
Many governments list specific requirements for emergency vehicle lighting. These requirements may address the colour, location and intensity/visibility of the lights, and whether they should flash or burn steadily. Laws also may regulate what vehicles may display these lights, and under what circumstances they may do so.
The warning lights may be of several types, which includes:
Audible warning devices.
When an emergency vehicle is responding, it often uses audio warning devices in addition to the visual warnings provided by its warning lights. Audio warning devices are turned off once the vehicle is on-scene. Such devices include:
Some emergency vehicle operators occasionally turn off their sirens when on side streets or when there are no cars on the road so as not to disturb residents; however, there is seldom a mandate for responders to do so. The driver will then turn on the sirens before proceeding through intersections or when traveling on potentially dangerous stretches of road.
Justification for use.
Anecdotally, the purpose of audible warnings on emergency vehicles is to enable quicker arrival on scene, and to promote safety of crews and spectators. However, rigorous scientific support for this position is very limited. A peer-reviewed study by Hunt et al concluded "the 43.5-second mean time savings does not warrant the use of lights and siren during ambulance transport, except in rare situations or clinical circumstances." In 2017, no scientific studies were found to weigh the benefits of sirens against the costs and hazards of the resulting urban noise.
Auxiliary lighting.
Auxiliary lighting is light used for illumination, to supplement factory-installed headlights or to illuminate areas to the side of or behind the vehicle. It is typically white or near-white light. Some emergency scenes require additional lighting if the emergency workers are to be able to effectively deal with the emergency. Also, building numbers are often obscured by darkness, making it difficult for emergency workers to find the scene of an emergency. For these reasons, emergency vehicles are often equipped with auxiliary lighting, such as:
Communications devices.
Efficient emergency responses require that emergency responders can communicate with a dispatcher, with each other, and often with other facilities (such as hospitals or public utilities). Emergency vehicles are equipped with the following types of equipment to do so:
Service/unit-specific equipment.
Different services require different types of equipment at emergency scenes (ambulances and fire trucks carry different types of equipment), and within one service, different units may require different equipment.
Fire.
Fire service units and their role differ between countries.