Auto Electronics


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Installing aftermarket vehicle security has always been a passion for trained mobile electronics installers, who have been waging a war of wits with car thieves for nearly 30 years. When talking about vehicle security, the first important point to make is that auto theft is a major continuing crime problem in the United States. In 2004, approximately 1.2 million vehicles were stolen in the United States valued at more than $8 billion[1], and more than one billion dollars worth of contents were stolen from vehicles[1], so the stakes are high. The automakers have been addressing the issue with factory (OEM) anti-theft measures designed to prevent “hot wiring” — typically these are transponder or resistance-based systems that look for the appropriate key in the ignition before starting. However, thieves are able to defeat these systems — according to the Highway Loss Data Institute, Cadillac Escalades are among recent model year vehicles most likely to have a theft claim, even though they are protected (adequately or not) by the GM Passlock II OEM anti-theft system. Clearly, there are limits to “factory security” — that's where the aftermarket comes in.

Aftermarket vehicle security differs from factory anti-theft systems in several key respects:

  • Every aftermarket installation is custom, as opposed to factory systems that are the same for each model year vehicle and are actually documented in service manuals.
  • Aftermarket vehicle security includes sensors where OEM security and anti-theft systems typically do not.
  • The aftermarket offers additional accessories designed to increase the security of the install.

These points are worth discussing in detail. An ideal aftermarket vehicle security installation is “stealth” — carefully hidden to make it harder to defeat. Wiring is disguised in the loom to look as “stock” as possible. The vehicle is partially disassembled and the CPU, siren(s) and other key components are buried deep out of sight. And, unlike factory anti-theft systems, they will never be in exactly the same place twice.

An aftermarket vehicle security system consists of a “brain” or CPU, which is typically installed in the passenger compartment, underneath the dash where it cannot be accessed without extensive disassembly. Either on-board or off-board, the brain is the primary sensor that comes with the system, which is typically a “shock” or impact sensor. For example, most Directed systems feature the patented (No. 5,534,845) dual-stage Stinger DoubleGuard shock sensor, which detects blows or impacts to the vehicle (likely to occur during a break-in attempt) that causes a magnet assembly to move in relation to a coil. An integrated circuit within the sensor then discriminates between light impacts (which cause the siren to chirp in the “warn away” response) and more substantial impacts that trigger the full six-tone siren to begin its cycle.

Besides connections to the shock sensor and siren, the brain is integrated with the vehicle using many other inputs and outputs as shown in Figure 1.

As you can see from the primary harness of the Viper 350HV, the security system is heavily integrated with the vehicle. The orange ground-when-armed output goes to the aftermarket starter kill relay, which prevents the engine from starting while the system is armed. The Light Flash Output flashes the lights to confirm arm and disarm, and also flashes them when the siren is sounding. Channel 3 is a programmable output for optional remote-control conveniences such as re-mote-control windows. Domelight Supervision lights the dome light for 30 seconds when the system is disarmed (a safety feature at night, to see inside the vehicle.) The trigger inputs are the “eyes and ears” of the system, allowing it to monitor the status of the vehicle. Channel 2 output is a validity output typically used for remote-control trunk release. In the case of the 350HV, there is no shock sensor input because the shock sensor is onboard the module.

That is the primary harness — the secondary harness is used for remote keyless entry functionality (Figure 2).

These are low current outputs intended to activate relays. Interfacing with the vehicle door locks is not a simple issue, and will be addressed later when we discuss digital vs. analog integration with the vehicle. Other harnesses include the status LED (which also serves as a visual deterrent, alerting thieves that the vehicle is protected), the valet programming switch, the programming tool port and the connection to the off-board antenna and receiver (which brings up the issue of range — more on this later, as well).

Besides the primary sensor that comes with the aftermarket security system, a number of other sensors are also available, for specific purposes. These include:

  • “Radar” proximity or field disturbance sensor. This is typically a 2.45 GHz dual-stage sensor that reacts to mass moving into the field using the Doppler Effect with either warn-away chirps or full siren. This sensor is ideal for convertibles.
  • Audio sensor. This sensor detects breaking glass using a microphone and sound discriminator looking for specific frequencies. It detects even “gentle” glass breakage that might not trigger the shock sensor.
  • Digital tilt sensor. This sensor detects if the vehicle is tilted more than two degrees, which would occur during either a towing or jacking attempt, and is suitable for protecting expensive tires, wheels and rims.
  • Closed loop sensor. This sensor triggers the siren if the loop is opened (disconnected) and is useful to protect tonneau covers, trailers, etc.
  • Magnetic switch. These switches can trigger the siren if, for instance, the sliding glass window in the back of a pickup truck or camper shell is opened while the system is armed.

In addition to sensors, the aftermarket offers a myriad of accessories designed to make it more difficult for thieves to steal vehicles. According to the National Insurance Crime Bureau, the more “layers of protection” between the vehicle and car thieves, the better. One of the most crucial accessories in the fight against auto theft is a backup battery siren. When this siren is hidden in a different location from the primary siren, it can continue to sound if the primary siren is silenced — even if the criminal disconnects the vehicle battery. Some other useful accessories include hood and trunk pins, passenger compartment “pain generator” sirens, electroluminescent “vehicle armed” indicators and additional immobilizers.

Other security issues are worth discussing: RF signal encryption, range and two-way communication with the system.

Following some “hot prowl” incidents in the late 1990s by criminals using illegal code grabber devices, which intercepted and retransmitted radio signals from garage door openers and car alarm transmitters, the aftermarket vehicle security industry became much more secure, resulting in Directed's current 66-bit encryption standard using 18 quintillion rolling codes (an 18 followed by 18 zeros), which appears to have solved the code grabbing problem for the time being.

Range is another important issue. Actually, the current push to extend FCC Part 15-compliant range from approximately one-quarter mile to the new state-of-the-art of a full mile has been driven more by the needs of remote start consumers than by strictly vehicle security, but the two technologies are closely related and frequently offered in tandem or “hybrid” combined systems. (Consumers in the cold weather regions of the country who want to start their engines by remote control to pre-warm them in the winter need as much practical range as possible to assure their vehicles start when parked down the street or at the far end of a snowy parking lot.) Thus, the current superheterodyne quarter-mile standard is currently transitioning to spread-spectrum technology (SST) up to a one mile range.

Finally, a related concern to range is confirmation (i.e., that the vehicle has armed, or that a remote-started vehicle actually started and is warming up), which has been addressed by two-way key chain remote controls — transceivers in-stead of transmitters — which use an LCD screen on the remote or flashing LEDs to receive confirmations back from the vehicle that the security/remote start system received the command and executed it.

Directed's two-way platform is called Responder and the Responder security and remote start hybrids use a digital FM standard called narrowband frequency shift keying (FSK) modulation at 433.92 MHz, which consists of a high sensitivity dual-conversion superheterodyne (DCSH) crystal-controlled receiver section with a surface acoustic wave (SAW) RF filter for interference rejection, and high-speed burst data transmission, which is capable of penetrating through interfering signals. A feature of Responder is the virtually instant pseudo full-duplex transmission and response to and from the vehicle. These systems are currently being upgraded to Responder SST, with projected -delivery this summer.


Integration of the security system with the vehicle is one of the technical challenges mobile electronics installers face in integrating the aftermarket system's keyless entry functionality with the vehicle door locks. Because of multiplexing (which saves hundreds of pounds of wire weight in each vehicle, improving gas mileage) and computerization, enabling remote-control operation of the door locks by analog outputs from the aftermarket system requires the installer to remove the driver's and passenger's door panels and to tie four diodes and two relays into each door's computer wiring by cutting, splicing and soldering, and then to do similar labor at the body control module (BCM). Because time is money, this obviously adds considerably to the cost of the install.

Digital options can dramatically streamline the installation: OEM integration modules that act as an interface between the vehicle's digital databus and the aftermarket system. This install requires power and ground and then typically a single wire to the databus, followed by a one-minute procedure to “introduce” it to the vehicle, so that the module will recognize the specific model year vehicle it is installed on and then broadcast the appropriate digital “words” onto the bus, commanding the door computers to lock and unlock the doors when the user pushes a button on the remote. Typical installation time is 25 minutes.

The current state-of-the-art changes almost monthly, but Directed's latest OEM integration advance is bidirectional communication on the controller area network (CAN) databus in VW and Audi vehicles, allowing the convenient installation of aftermarket vehicle security and remote start in vehicles that were off-limits before because of severe labor intensity. True bidirectional communication on the CAN bus allows an aftermarket remote to control a variety of factory systems on the vehicle, including lock and unlock, factory alarm arm and disarm, windows open and close, trunk release and driver's priority unlock. Additionally, CAN1 can turn the headlights, parking light flash, hazard lights and radio on or off. CAN1 can also read the engine speed and brake pedal and provide outputs for use with aftermarket remote start systems (all features “when available” per model/year). CAN1 comes with a universal harness and a T-harness that will allow CAN1 to plug into most Directed systems with a 12-pin main harness.

Because the CAN1 interface is bidirectional, the flip side is that the factory transmitter can be used to arm and disarm an aftermarket security system that is designed to work with the factory transmitters. For a simple power, ground and one wire data connection, the number of inputs and outputs provided by the module is surprising (see Figure 3).


  1. FBI Uniform Crime Report, National Insurance Crime Bureau, Sourcebook of Criminal Justice Statistics.


Kennedy Gammage is the corporate communications manager for Directed Electronics. He can be reached at [email protected].

Innovations award

Directed won an Innovations award at the 2000 Consumer Electronics Show (CES) for its Jeep Interface Module (JIM) part number 455J, one of the earliest aftermarket databus modules. The JIM operated on the SAE J1850 databus using VPW protocol, broadcasting 56-bit digital words at a 10.4 kHz data rate. As with all Directed databus modules, the JIM implemented bit collision detection, to assure that the bus is clear when commands are sent, thus avoiding packet collisions and other data interference that can cause problems in the BCM.

New training facility

Directed is a supporter of the industry Mobile Electronics Certified Professional (MECP) program, winning Proctor of the Year honors repeatedly, and MECP Manufacturer of the Year. Last year, Directed took its commitment to professional development of mobile electronics installation training to a new level with the opening of its professional installer training facility, The Snake Pit. Now in its second year, and expanding in size and curriculum in 2006, The Snake Pit represents a multiyear, multimillion-dollar “giving back” to the industry, by helping to develop hands-on, the next generation of mobile electronics installers, who will be able to take this story to the next level.

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