The car alarm system must be effective as protection against theft, convenient to use and reliable. Taking into account these requirements, you can create a vision of the perfect device, and when choosing a specific solution, evaluate it with the measure of the ideal. A good alarm should fulfill basic functions and be expandable. The number of additional functions cannot be too large, because it complicates its operation. Users usually don't have the time or willingness to learn how to deal with an alarm, and in emergency situations or threats will be guided by logic, not the instruction manual.
An ideal car alarm should have the following functions:
♦ cover all vehicle openings (door, engine cover and trunk);
♦ protect the interior (reaction to glass breakage, movement inside, body tilting);
♦ secure the engine against starting;
♦ operate the central locking of the doors (if it is equipped with the car);
♦ close the door locks while driving (protection against intrusion into the car, eg. when parked under traffic lights);
♦ close windows on activation (if the car has electric windows);
♦ blocking the alarm should be done by entering the PIN code (np. when returning the car to a service station) according to a simple and unambiguous procedure;
♦ require additional anti-robbery authorization.
The anti-hijack function is an additional authorization of the alarm and immobilizer that protects the vehicle against a robbery attack. After deactivating the protection, the device checks, whether the person using the car is entitled to do so. Additional authorization can be done by pressing a hidden button (inconvenient and observable activity) or reading the code from an additional transponder, which the owner carries with him independently of the remote control controlling the alarm. If the driver is forcibly removed from the car, the security system will not be additionally authorized, the sound signaling system will be turned on, and the engine is immobilized by the immobilizer. Use of the remote control (usually attached to the ignition key) until the alarm is deactivated again without additional authorization, it will not be possible to disable the signaling and start the engine.
For convenience, the car alarm should be controlled with a remote control. Its housing must be impact-resistant, dampness and prevent accidental triggering of the control signal. The remote control is carried in a pocket together with other keys and trinkets, sometimes it will fall out of your hand on the ground or be spilled with coffee; in such conditions it cannot be damaged. It is best if the remote control generates a radio signal, which does not have to be aimed directly at the car's code reader. The signal must be dynamically encoded, which protects the vehicle owner from scanning the code by a thief and using it to deactivate the security. The range of the remote control signal should not exceed the distance 10 do 20 m. A greater range creates a risk of "vulnerability" of the vehicle over time, when the owner, after unlocking the system, comes to him. Another important feature of the remote control is its power supply. Such constructions should be selected, in which the used batteries last for two years or longer.
For the convenience of use, the remote control should be equipped with one easy-to-use button. Pressing it activates the alarm, it disconnects the circuits protected by the built-in immobilizer and if the car design allows it, it also closes the windows and locks the central door lock. Using the same button again unlocks the immobilizer circuits, opens the locks and deactivates the alarm sensors – the car is ready for use. Moreover, the button on the remote control should be the only element of the user's communication with the security device, this will guarantee correct operation in the event of a failure.