What are ultrasonic car alarm sensors?
Ultrasonic sensors detect movement in the internal space of a vehicle. They are very effective in detecting an intrusion so are commonly used with car alarms systems.
When it comes to protecting your vehicles cabin, ultrasonic sensors perform better than glass break sensors, which are simply not effective if you have window tint film or a larger cabin.
How do ultrasonic sensors work?
There are normally two sensors, these are typically installed at the top of the “A” pillars. One sensor transmits a high pitch sound wave (ultrasound) which is inaudible to the human ear, and the other sensor receives the signal.
The sound wave reflects around the vehicle and is received by the second sensor. If the wave pattern changes from the initial one learnt during the pre-arm period (typically about 25 seconds), then the alarm system will trigger.
Avoiding false alarms - Don't leave your windows open!
Close the window or disable the sensor
A gust of wind through a slightly open window has the potential to be picked up by the sensors and trigger the alarm. This can be solved with a window closure module.
If you do wish to leave a window open and arm the alarm then you will need to turn off the ultrasonic sensors when you arm the alarm to prevent a false alarm.
Which alarms allow you to turn off the ultrasonic sensors?
I recommend Vodafone Automotive (Cobra) and Autowatch alarms. The models that come with a remote allow you to turn the ultrasonic input off by pressing the arm button on the remote a second time upon arming.
Some Viper alarms also allow you to turn off the sensors this way too.
Intelligent CAN-BUS systems
Some CAN-BUS alarms are able to detect if a window is left open. They will chirp the siren upon the alarm being armed to warn you and disable the ultrasonic sensors to avoid a false alarm.
European cars often include window open data
This feature is usually found on German vehicles. it works the same as you’d expect from the factory alarms, but is only available if the vehicle has the window data, and the alarm firmware is programmed to read it.
Sadly not all vehicles report if a window is left open, but the better alarms out there do allow you to turn the Ultrasonic sensors off when you arm the alarm.
Turning off the ultrasonic sensors manually
If you’re not lucky enough to have your window position recorded by the CAN-BUS then all decent alarms have a manual way to disable them.
This is usually in the user manual. I’ve also made a series of videos on my YouTube channel with guides on how to turn off the various sensors.
Fitting Ultrasonic Sensors
Installation details
I take pride in making sure that the ultrasonic sensors look like they came with the vehicle. This starts with making sure that the location is perfect, checking that everything is symmetrical and then double checking again before I commit to drilling any holes.
Obviously I need good quality sensors to be able to do this. Some sensors just don’t look good and you’re fighting a losing battle to make them fit nicely.
A good install starts with a good product
Part of my job is recommending the right system, If your installer does not bother to address the basics then the rest of the alarm is unlikely to look, or perform well.
Car alarm sensor installation care
It’s the hidden part of the installation that really matters.
Despite the cables being hidden behind the trim, it is still important to make sure that they are run nicely to make sure that the don’t get pinched, plus secured to make sure that there are no rattles.
I like to leave a loop at the trim joints to make it easier for anyone who works on the vehicle at a later date. This way there is less chance of damage being done in the future.
There is nothing more frustrating than having to work around someone mess from a previous install. It’s super annoying when you find that the windscreen installer has got carried away with the silicone and glued up the A pillars! Or that the car audio guy has just tucked a cable without securing it.
It’s best practice to think about the next guy.
Best ultrasonic car alarm sensors?
In my opinion the clear winner is Vodafone Automotive, formally called Cobra. Their sensors look great and work well.
They can be be programmed to suit the vehicle interior size, and can even be turned off via an external input
Here are some photos I’ve taken to show how well the match the existing vehicle trim, You’d be forgive for thinking they were installed in the car from factory:
Vodafone Automotive ultrasonic sensors
Two styles of movement sensors to pick from
The latest generation of sensors from Vodafone Automotive work with the excellent 4822. They come in either flush mount pods, or A pillar capsule that suit the interior or most cars.
The flush mount ones come in both black and grey, but the A pillar ones only come in grey.
That said, not all cars have a grey A pillars and they can look silly if the car has black trim.
Colour coded sensors
The good news is that they can be painted to match. I try to carry some pre-sprayed black capsules with me to cover this at installation time.
It’s worth noting that the Vodafone Automotive sensors only work with their alarms so can not be used on other brands as the sensors plug directly in the alarm control unit.
Factory ultrasonic location spots
Some vehicles have factory ultrasonic slots available. This is sometimes the case in lower spec models where an alarm is an optional extra.
I love using these as it makes for a super clean installation that looks exactly as it would as an original specification alarm.
Not suitable for all vehicles
Ultrasonic sensors are not suitable for vehicles that are not sealed such as rag-top convertibles.
If you have a cloth top car, then a microwave sensor would be a better solution.
Other brands of aftermarket ultrasonic sensors
These don’t look factory installed
If I’m not installing a Vodafone Automotive alarm, my go to sensors are either Autowatch 632 or DEI 509U (Viper).
Both brands make stand alone sensors which can be added to their alarms, most of their alarms give you the option to disable the sensors upon arming.
Autowatch 632 intelligent ultrasonic sensors
These are a plug and play option for all current Autowatch alarms, but there is nothing stopping a good installer from chopping the plug off and wiring them up to any other brand of alarm.
All of the Autowatch remote alarms allow you to turn off the sensors by pressing the arm button a second time when setting the alarm.
Directed Electronics 509U ultrasonic sensors
The 509U sensors are made by the firm behind Viper. The sensors come with a couple of mounting options. They can either be screwed in place, or have the option of a clip which can be tucked in the A pillar trim gap.
Aftermarket car alarm sensors
If you are fussy like me then may not want to have sensors that are clearly retro fitted.
The 509U does the job fine and can work with other alarms, but, like the Autowatch 362 look very aftermarket in appearance.
Risk of pinched cables
With the 509U the cable needs to be tucked into a gap so does not have the clean look. Personally I’m not a fan of tucking cables into gaps as they can get pinched. As with all cables, it’s something to be aware of when doing an installation.
The advantage with the Vodafone Automotive sensors is the cable disappears out the back and make for a much cleaner install.
FAQs
Do ultrasonic sensors drain a car battery?
No: typically they draw about 6mA when armed. Compare that to a PIR sensor that draws 8mA constantly.
Can ultrasonic sensors cause false alarms?
They can do if you leave a window open as explained here.
Are volumetric sensors different?
No, they are the same sensor but with a different name, Ultrasonic sensors are sometimes called volumetric sensors as they can detect a change in the internal volume of a vehicle.
Best car alarms with ultrasonic sensors?
- Any Vodafone Automotive or Cobra alarm
- Autowatch 446RiSU
Which alarms should be avoided with ultrasonic sensors?
Any RhinoCo alarm (AVS) as sensor disable is not a programmable option. Besides which they are not good alarm systems!
How much do ultrasonic sensors cost?
- Vodafone Automotive $100.00
- Autowatch 362 $160.00
- DEI 509U $150.00
