Clio 182 alarm, three blinks (Ultrasonic?)

[plasticmorph]

Hi, My alarm has just gone off and I'm trying to work out what caused it. It was blinking three times on the LED inside the car which going by a guide on here, is the untrasonic sensors on the pillars. I take it these are not just PIR's so what triggers them and how do they work? The doors had not been opened.

What sensors would be triggered by a branch falling off a tree onto the car, or a very loud chav-mobil going past?

 

[Steven103]

Very "durrr" suggestion I know, but were the windows open? Someone walked past my car the other day when the ultrasonic sensors were pointing out the window and that triggered the alarm.

I'm assuming it's just an electromagnetic wave (in the "ultrasonic" region of the spectrum you'd guess...) which is emitted/timed/received once you lock the car. I.e. invisible beam which makes loud noises when it's "cut"

 

[plasticmorph]

Haha windows were shut! Cheers!