How Do Microwave Sensors Work?
A microwave sensor is ideal for soft top convertibles or other areas where ultrasonic sensors would not be suitable. They are not sensitive to air movement.
The sensor operation is based on the “Doppler effect” principle according to which a moving conductor object hit by electromagnetic waves at high frequency causes the beam to be reflected in a different way. If the reflected waves are measured the foreign body can be identified and an alarm signal can be generated.
Where to installer a microwave sensor
Normally the sensor would be located in the centre of a car. This is generally the best spot to detect if someone reaches in through the roof or an open window. But there are other ways to install one as I shall explain soon.
The sensor can be adjusted to suit the vehicle and location. A small mass (such as a Human hand) will need to be close to the sensor to trigger it. A large mass such garage door moving overhead will be detected further away.
How microwave sensors work in a vehicle
The sensor creates a virtual bubble, but will not detect beyond an existing metal object such as a car door.
It is vital not to have any metal obstruction close to the sensor. For example,fitting one below a pocket where coins maybe stored is not ideal.
The Microwave can be adjusted in range up to about 2 meters. It can be hidden under upholstery or dash panels depending on material.
It’s worth noting that cell phones can interfere with a microwave sensor. Do not leave your phone in a storage area in close proximity to the sensor when the alarm is armed.
Possible Locations and uses
- Central transmission tunnel under trim
- Behind rear seat
- Roof panel facing downwards
- Ute trays
- Boat alarm (See below)
- In door (See below)
Custom made boat alarm with a microwave sensor
As shown in the photos, I lined the case with tin foil before fitting the microwave sensor in. This way it would only detect objects in front of it. The unit was mounted in the fibre glass hull at the stern of the boat behind the entry steps.
The case is fully waterproof as was the external Cobra siren. The buttons on the case of the box are simply for any future programming.
AC Cobra with Cobra alarm (What else would you use?)
I used a similar trick with tin foil in a AC Cobra replica recently. The carpet door liner was removed from the fibre glass door. It was then lined it with foil before fitting the sensor and re upholstering it.
This allowed someone to walk past the door without upsetting the alarm. As soon as the door is opened it would detect the person trigger the alarm. The range was set to detect anyone getting in via the other side too.
It was a very tidy install where the car had no door switches to wire up to. Retro fitting them into a fibre glass body was not a viable option.
Alterative car alarm sensors
I supply and install a whole range of car alarm sensors, part of my job is explaining how they work, and which ones are the most suitable for your vehicle
