public order crimes; hold and reinforce a police barricade to keep the scene contained; or simply transport officers and equipment at the scene in a manner safer than what could be achieved with a standard police car. Common modifications include tear gas launchers, shields, and caged windows. Some riot control vehicles also include less-lethal weaponry and devices, such as water cannons and long-range acoustic devices. Community engagement, liaison, and demonstration vehicles A community engagement vehicle, also known as a liaison vehicle, demonstration vehicle, or parade car, is a police car used for display and community policing purposes, but not for patrol duties. These are often high-performance, modified cars, classic police cars, or vehicles seized from convicted criminals and converted to police cars, used to represent the agency in parades, promote a specific program (such as the D.A.R.E. program), or help build connections between law enforcement and certain groups that the vehicle appeals to. Some cars can be visibly marked but not fitted with audio or visual warning devices. These are used by community liaison officers for transport to engagements and making appearances at community events. Some vehicles are produced by automotive manufacturers with police markings to showcase them to police departments; these are usually concepts, prototypes, or reveals of their police fleet offerings. Emergency light and siren manufacturers such as Federal Signal, Whelen, and Code 3 also use unofficial police cars to demonstrate their emergency vehicle equipment. Equipment Police cars are usually passenger car models which are upgraded to the specifications required by the purchasing police service. Several vehicle manufacturers provide a "police package" option, which is built to police specifications from the factory. Agencies may add to these modifications by adding their own equipment and making their own modifications after purchasing a vehicle. Mechanical modifications Modifications a police car might undergo include adjustments for higher durability, speed, high-mileage driving, and long periods of idling at a higher temperature. This is usually accomplished through installing heavy duty suspension, brakes, calibrated speedometer, tires, alternator, transmission, and cooling systems. The car's stock engine may be modified or replaced by a more powerful engine from another vehicle from the manufacturer. The car's electrical system may also be upgraded to accommodate for the additional electronic police equipment. Warning systems Police vehicles are often fitted with audible and visual warning systems to alert other motorists of their approach or position on the road. In many