Most traditional car alarms come with a remote, but if you already have a remote built into your car key you should probably consider a PLIP alarm.
So what is a PLIP alarm?
A PLIP alarm is a car alarm that is designed to work with the vehicles existing keyless entry system. So it works with the existing remote control or passive keyless entry proximity system. They are also known as an OEM upgrade alarms. They negate the need to have a separate remote control on your keyring so are simple to use.
Technically you could include CAN-BUS alarms as an OEM upgrade, but for this post I’ll explain how these alarms work for vehicle where a CAN-BUS alarm is not an option.
How do Plip alarms work?
Most PLIP alarm are wired up to the vehicles central locking actuator wires so they arm when the vehicle is locked, and disarm when the vehicle is unlocked.
Then it’s a case of wiring up the doors, and bonnet, and any additional sensors to trigger the alarm should a break in occur.
However, it’s not that simple as you don’t want the alarm to disarm when the vehicle is unlocked without the remote control.
Good PLIP alarm installation
Having the alarm disarm with the lock snib, or the door lock switch, or even the key in the door makes the alarm easy to defeat.
Less critically, you probably don’t want it to arm from the internal door lock button either!
How to Prevent a "None Remote" Disarm?
There are two basic methods this is achieved. The first is the Inhibit Mode where the alarm will not disarm if it sees any activity from then lock switches.
This prevents the alarm from arming or disarming using the key in the door. It also stops the alarm from disarming with the door lock snib, or the door lock switch.
The other common method used when installing PLIP alarms is the Enable Mode. This monitors the hazard lights as well as the door lock actuators. When the alarm sees both commands in sequence it will arm and disarm.
The issue with this method is that the PLIP alarm needs to be wired so it can’t be cheated into disarming by pressing the hazard switch and unlocking the doors.
Testing Your PLIP Alarm
Part of my job as a vehicle security installer is to make sure that the alarm can not be tricked into being disarmed.
If the alarm disarms with the key in the door, or by flicking the lock snib then I have failed to do the installation correctly.
Effective OEM upgrade car alarms
There is not much point in having an alarm if disarms when the door lock is picked or attacked by brute force.
It’s not just poorly installed PLIP upgrade alarms that have this issue. There are heaps or factory car alarms that simply disarm with the key in the door lock, including my own vehicle!
How Stuff Works has a good page about how remote entry works if you are interested.
