Magnetometer or not
Many driveway alarms use a magnetometer. A magnetometer is a strip that needs to be buried just beneath the ground surface across the width of your driveway. These devices simply detect the presence of a metal object such as a car passing across them. Unfortunately these cannot detect the difference between a car and a bicycle and they do NOT detect people. In addition, in the UK, most driveways are paved and using a system with a magnetometer will mean digging up expensive paving.
Magnetometers are the most reliable method of detecting vehicles entering a site. PIR detectors, even high quality units designed for external use are not great at detecting vehicles. This is because although the engine may be warm, the bodywork such as the wings and side panels are usually the same as the ambient temperature.
Good external PIRs will usually detect a vehicle if it is moving slowly enough. Examples of this are –
- A car pulling in to a short driveway or
- A car that has to turn in to a driveway. This requires the car to slow to just a couple of mile an hour.
If you need to secure a very long driveway or an access road, a magnetometer or a set of ‘Active Beams’ is the best option.