An Alarm microwave sensor (or super high-frequency volumetric sensor as Cobra call it) is ideal for soft top convertibles or other areas where ultrasonic sensors would not be suitable. Microwave Sensors 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.
Normally the sensor would be located in the centre of a car to detect if someone reaches in through the roof or an open window. However, 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 closer to the sensor to trigger it than a large mass such garage door moving overhead.
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, so areas, where coins may be stored, are not ideal.
The Microwave can be adjusted in a range up to about 2 meters and can be hidden under upholstery or dash panels depending on the material.
It’s worth noting that cell phones can interfere with a microwave sensor so 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 the trim
- Behind rear seat
- Roof panel facing downwards
- Ute trays
- Boat alarm (See below)
- In the door (See below)
Custom Boat Alarm
One of the more interesting jobs I have recently done is a boat alarm. For this, I placed all of the components in a watertight box as shown below
I lined the case with tin foil before fitting the microwave sensor. This way it would only detect objects in front of it. I mounted the box in the fibreglass hull at the stern of the boat behind the entry steps.
The case is fully waterproof as was the external Cobra 4310 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 an AC Cobra replica recently. First I removed the carpet from the fibreglass door, then lined it with foil before fitting the sensor and reupholstering it.
This allowed someone to walk past the door without upsetting the alarm, but as soon as the door is opened it would detect the person to 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 use. Retrofitting them into a fibreglass body was not a viable option.
Cobra 5462 Super High-Frequency Volumetric Sensor
Works as dual zone sensor with some Cobra alarms