PIR sensors (passive infared) detect infared light (heat energy) which radiates from objects in it’s field of vision such as a human body. This makes them great for protecting Ute canopies or the back or vans where a solid cargo barrier prevents Ultrasonic Sensors covering the space.
There are two ways to connect a PIR sensor up to an alarm. The first method is to wire the sensor up to the alarms AUX input. Most decent alarms give the user the option to disable the AUX input on the alarm whilst still having door and bonnet triggers active so that the vehicle can be locked and armed with the PIR sensor turned off if desired.
Upgrade alarm method
One common issue when installing a PIR sensor with an upgrade alarm in a Ute is that when the vehicle is unlocked (alarm is disarmed), the vehicle will re-lock and in turn re-arm the alarm if a door is not opened after a set time (normally about 30 seconds).
This can then catch the owner out if they only wish to access tools or such in the canopy and not access the main vehicle. As soon as they trigger the PIR sensor then the alarm sounds! Whilst the user could simply open and shut one of the doors to stop this from happening most people don’t find this vary convenient.
Wiring the PIR sensor via a relay to one of the doors will trick the vehicle into thinking that a door has been opened as soon as the PIR sensor detects movement. This will then prevent the vehicle from re-locking and re-arming, and getting triggered by mistake.
The down side to the method is that you need to be aware and remember how it works. Also having a dog in the back would cause the door open warning light to flash each time the dog moved which would also turn the internal lamp on and off! There is a better solution:
Remote Double Tap Module
The Remote Double Tap Module works with the existing remote and simply prevents the vehicle from re-locking if the remote unlock button is pressed twice. It can also be used to unlock the canopy where electronic locks are fitted. More details here….
Autowatch make a wireless PIR sensor. Details can be found here: http://vehiclesecurity.co.nz/blog/autowatch-wireless-p-i-r-sensor