How effective are oem add on alarms?

I recently spoke with an installer about doing an oem add on alarm kit for my 07 Avalanche that has factory alarm and remote start since I want to use the factory keyfobs. My questions are this, since the arm and disarm utilizes the driver door lock unlock, if a theif punches the lock and turns the cylinder does the oem and add on alarm kit both see this as a key and disarms? Secondly he stated I didn't need any bypass. So how does the add on alarm kit starter kill relay allow the remote start to function without a bypass and the alarm still being armed?"ole blake"

It is hard to answer your questions as we have no way of knowing what the installer is looking to install. This question has really gotten me and some other installers thinking as you are correct. We generally assume that people will break the glass on a vehicle to get in, but punching the lock cylinder would allow you to disable the alarm if you were able to turn the lock cylinder as that will disable the OEM alarm as well as the aftermarket alarm IF it is connected to the OEM disarm/unlock wire. The only way around this would be to add an aftermarket alarm that connects to the lock and unlock MOTOR wires as these would not see a pulse when turning the lock cylinder. The downside to this is that by pressing the Unlock button you can disarm the system. Ideally a basic alarm that does not connect to the can bus but uses an aftermarket keyfob would be the best way as it would be connected via analog connections and in no way influenced via the can network. Since you are wanting an OEM keyfob to control it you will have to know there will be limitations to the system.

Cobra in Italy made OEM style alarms that worked off the motor wires just as described. Very hard to beat. This was pre-CAN, current DEI and Cobra for Europe are CAN. The downside back then was the OEM remote's range or lack of. As a side note I no longer install (age etc.) but when I did using what was available here in the UK, with DB-ALL2 I turn OFF OEM fob control or go W2W.

There are systems that work well by converting the factory keyless to activate an aftermarket alarm. As mentioned they connect to the driver's door lock wires. The add on alarm will arm/disarm only when using the factory remote. It connects to the driver's door lock motor wires. They work provided your vehicle is programmed for driver door priority (only driver's door unlocks on first press of remote's unlock button - all doors unlock if unlock on remote is pressed a second time within 5 seconds). It works because the system is connected to the unlock switch on the inside of the door. If the inside switch is used to unlock the doors, the alarm ignores it and won't disarm. The factory alarm will disarm if the key cylinder on the outside of the door is manipulated to unlock, but the add on alarm won't. Your big problem is that the only benefit of the add on alarm is the ability to add a shock sensor or other additional sensors. YOU CANNOT use your factory remote starter though. The add on alarm will trigger if you remote start the vehicle. You have 2 options. You can either install a full function alarm/remote start combination system. It will have it's own remotes with better range. It can lock/unlock the doors and arm/disarm the factory alarm and the new alarm. The new unit is designed to take the shock sensor off line during remote start and will still monitor the doors. These units cost quite a bit as you are adding a lot of parts. Your other option is GM used to offer an add on shock sensor system and a tilt sensor. They were sold as a GM accessory option. The GM dealer must install it as the vehicle needs to be reprogrammed for it to work. The sensors are designed to go off line during factory remote start as this is done when reprogramming the vehicle. I'm not sure if they are still available but you can ask your local GM dealer to look into it.sparky

sparkie wrote: There are systems that work well by converting the factory keyless to activate an aftermarket alarm. As mentioned they connect to the driver's door lock wires. The add on alarm will arm/disarm only when using the factory remote. It connects to the driver's door lock motor wires. They work provided your vehicle is programmed for driver door priority (only driver's door unlocks on first press of remote's unlock button - all doors unlock if unlock on remote is pressed a second time within 5 seconds). It works because the system is connected to the unlock switch on the inside of the door. If the inside switch is used to unlock the doors, the alarm ignores it and won't disarm.

I don't see by how you have this explained that it would not disarm the system by pressing the unlock button. If you have it connected to the motor wires then anytime the motor wires are engaged it will arm/disarm even if you press the button in the vehicle. Maybe I am missing something, can you explain this for me?

The system I use is a Code Alarm 3051. It is designed to connect to the driver door lock motor wires as well as the wires from the power door lock switch. Vehicles that have the option of driver door priority (only driver door unlocks with first press of the unlock button on the factory remote and all doors on 2nd press of button) are wired where the driver's door lock motor wires are isolated. The motor wires rest at ground. One wire receives 12 volts for lock and the other will get 12 volts for unlock. The vehicle isolates them by means of a relay or module. When you use the factory remote, only the door lock motor wires have power and ground. The wires from the power door lock switch are not used. When you use press the unlock button on the factory remote twice usually within 5 seconds the keyless entry module or BCM in the vehicle activates the same wires that are connected to the power door lock switch to lock or unlock all doors. The alarm has arm/disarm input wires. The arm input goes to the drivers door lock motor wire that goes to 12 volts when locking. The first disarm wire for the alarm goes to the driver's door lock motor wire that goes to 12 volts when using the factory remote to unlock the drivers door. The second disarm input for the alarm goes to the power door unlock switch that activates when you use the switch inside the vehicle. If the alarm sees BOTH the switch wire for unlock and the driver's motor unlock wire activate together, it will not disarm the alarm. The system only works for vehicles that isolate the driver's door lock motor. It will not work on a vehicle that unlocks all doors with one press of the unlock button on the factory remote. The power lock switch wires don't activate when using the factory remote to unlock the doors in vehicles that have driver door priority. It hard to explain, but it works for many vehicles. It's not designed to work with vehicles with factory remote start though.sparky

RS Specialist: What you're unaware of, and Sparkie mentions in the post above, is that these add-on systems have an additional input called "disarm defeat". If the system sees a signal on this wire at the same time as an UNLOCK signal on the driver door, it won't disarm. The disarm defeat is connected to the passenger UNLOCK or door switch UNLOCK. DEI add-on alarm systems are intended to work with OEM systems that have driver priority unlock. The add-on system has 3 wires that connect to the lock motors. One to LOCK (for ARM), one to driver door UNLOCK (DISARM) And "disarm defeat" which goes to PASSENGER unlock. If the system sees an unlock signal on both wires, like when the door switch is used, it won't disarm. I've studied this system because I have one on my desk I want to install in my Typhoon and retain the OEM fobs. I don't feel honking horns do squat. But there are all kinds of things to do with the GWA that will make a theif give up.