There are a number of different terms to describe the many technologies in movement detection today. Each manufacturer has their own breed of sensors using different technologies, different lenses, combinations of technologies and many different shapes and sizes of detectors - each trying to sound better and out perform the rest.

In general there are only two common types of technologies used in movement detection today - that being Infra-Red sensors and Microwave sensors.

Infra-Red sensors look at the infra-red temperature of the room and detect any changes in the infa-red temperature (or radiation). Animals, people, air-conditions, heaters all absorb, and radiate heat (ie infra-red), and so these are all detectable by a Infra-Red detector. Most sensors have a lens or a mirror that focuses an infra-red image of the room onto a small semiconductor component called a Piro. It’s this Piro that sensors the changes, and therefore decides if there is movement in the room.

Microwave detectors work more like a 'ping' is used in submarines. A microwave signal is sent out by the sensor and then received back by the detector. This pattern is repeated continuously, and as long as there is no changes to anything in the room, these signals should remain uniform as they bounce around the room and then are reflected back to the sensor for analysis. When something solid moves in the room, these signals vary as the object moves around. It’s this variation in signals that allows the sensor to detect movement.

Now you know the basics of how sensors can detect movement, lets look at some specific sensors that are available with our kits and where and how they should be used.

Both the Blue Line PIRs and the Classic Line PIRs use infra-red Piro’s to detect movement in the coverage area. Although there is a great amount of technology in these sensors, they are the simplest and cheapest forms of movement detection. These sensors can be used very successfully in the average home or office environment and have an exceptionally low false alarm rate when used and installed correctly. As well as people, they can of course also see animals, air-conditioners, heaters (only when they on of course!) and any wind currents. So if you were planning to leave the dog in the house with the air-conditioning on, these sensors are obviously not the ones to use. However, the average office and home doesn’t have pets and doesn’t have the air-conditioning on when you are out. The majority of panels we install use these basic detectors, and we have thousands upon thousands working day in day out in the field without issue. They are extremely reliable in their correct environment.

The Dual or Quad PIR works on exactly the same principles as the normal infra-red detector above. So what makes this sensor different and better? These sensors use two Piro’s next to each other in the same detector instead of a single Piro on it’s own, like the detector above. Both Piro’s have the same infra-red image focused on them, and both Piros simultaneously and constantly are looking for changes in the infra-red radiation in the room. The signals from both these Piros are digitally analysed and compared to each other. Only when both Piro’s simultaneously detect the same movement and provide the same signal pattern does the sensor go into ‘alarm’.

These sensors are great for more harsh environments like sheds, garages, area’s of high or heavy traffic, houses near boats or harbours or any area where there is more electronic interference that might impede the sensors performance.

If you don’t have a tight budget, we recommend using quad sensors for all our kits.

Tri-tech detectors (also known as Dual-Tech detectors) use a combination of technologies for superior false alarm suppression in very harsh environments, or areas where a normal PIRs is generally known to give false alarms. These detectors use a normal Piro to detect infra-red movement, but also simultaneously use a microwave transmitter / receiver to detect the movement in a totally different way to that of the on-board Piro. Only when both of these technologies in the detector sense movement concurrently does the detector go into ‘alarm’.

The advantage of using microwave technology is that it’s unaffected by wind currents, air-conditioners, heaters and the like. These detectors also have the ability to calculate the mass of the objects moving, and in some detectors can analyse this information against a table of previously learnt signals to distinguish against interference or genuine signals, or animals. This means you can use it with the air-conditioning on, in a wooden or brick shed that that isn’t sealed very well, roof spaces, harsh environments and you can also use it with pets.

Generally we would describe sheds / barns / store rooms as a harsh environment for a detector. The commonly are sealed very badly, have birds, rodents and breezes randomly through them and are a breeding ground for false alarms - ‘Put in the best detector’ I hear you say. Yes, in most cases this is true, and a Tri-tech would be the way to go. The only disadvantage of the Tri-tech is its ability to see metal objects very well, as they reflect microwave energy very well, and in some cases does cause false alarms from the microwave. If your shed is made from metal, the best senor would be a Quad. If you have a brick or fibro shed, the Tri-tech is the way to go.

In general, and as far as possible, all sensors should be installed on the outside wall of a room looking into the room, not in a inner corner of the room looking out.

Although PIRs can’t see through glass, if it is facing a window you could get false alarms from curtains moving or by having direct sunlight on the sensor. Remember that the sun will move during different seasons, and although you might be sure the sun won’t shine on it now, it might do during another season.