Car Alarm Siren - The government tends to have standards on vehicle-mounted sirens. An example of this would be in California where sirens are designated Class A or Class B. Without all of the technical terms, a Class A siren is so loud that it is able to be mounted nearly anywhere on a vehicle. Class B sirens are not as loud and have to be mounted on a plane parallel to the level roadway and also parallel to the direction the vehicle travels when driving in a straight line. In certain cases car alarm sirens have to be approved by local agencies. An example of this is that the California Highway Patrol has to approve specific models for use on every emergency vehicle in the state. The approval is important because it ensures that the devices perform correctly. Using unapproved devices could be a factor in determining the fault of a collision if it occurs. Siren speakers, or mechanical sirens, should be sure to be mounted ahead of the passenger compartment. This will reduce the noise for occupants and it also makes two-way radio and mobile telephone audio more accessible during siren use. It also puts the sound where it will serve a useful purpose. In some of the high end designs there are some more parts, such as the radio receiver, that facilitates the wireless control of a car and the second one is auxiliary battery when the car’s main battery is not functioning. This auxiliary battery helps the alarm system operate. The third part is the computer control unit. This unit monitors everything that is happening in the surrounding areas of the car and if by chance there is something unwanted, it will blow the car alarm siren off. Normally, when the alarm system is triggered, there will be two different reactions. A warning sets off a short siren and blinkers signal for 0.5 sec. or the alarm siren will sound for up to 30 seconds and the turning indicators will flash for 60 seconds. Panic alarms and sirens can also be triggered by remote control.