Puzzled,over infrared?

[tblo163]

I've got a Sparkright alarm fitted to my car,every night about the same time it goes off.(usually about 2.00am)for no apparent reason.I've set the sensitivity as low as possible,but it's still no better.I know there is nothing wrong with the unit,so the only conclusion is that there is some kind of infrared signal being transmitted from an unknown source.I am aware that it is possible to activate any appliance that is controlled by remote,by re-tuning.this theory is proven by my remote controlled electric fire,which reacts when opperating my DVD Player.So the problem now is,if I can't find the source responsible for activating my alarm,can I re-tune my alarm & remote control to a new frequency ? another thing I have noticed,is that my freeview tuner flashes when this problem occurs(even though it's in stand-by)So it looks like some kind of air-borne transmition.I just cannot get my head round this one.Any ideas ?

 

[Nigel Goodwin]

Well they don't use different 'frequencies', IR remotes use digital coding transmitted on top of an ultrasonic modulation, usually around 38KHz.

Your alarm and remote will use a specific digital code, usually set my tiny DIL switches, so you may be able to alter both to a different setting and see if that helps.

However, IR is short range and highly directional, you could try placing an object in front of the sensor to try and find which direction it's coming from.

 

[picbits]

It could be that at 2am its the coolest time of night and your car battery voltage drops causing the voltage drop sensor in the alarm to trigger.

It could also be that there is something transmitting a strong radio signal at this time

Possibly a load of houses switching over to economy 7 at the same time causing an EMI spike

You might even find its a bunch of drunkards coming back from the nightclub at kicking out time .......
Chances of it being IR related are extremely remote (pardon the pun)

 

[crutschow]

Does the Sparkright use IR or RF for the remote?

 

[picbits]

Most of the older ones used IR

 

[tblo163]

That sounds very fiesable,the alarm does in fact use IR.Thinking about any voltage surge (or otherwise) this could be the cause,any residual voltage in any of the systems would have drained by this time,the only thing running is the clock,normally this would not set the alarm off,however there is a fault with the clock,it's running slow,you can hear it ticking,and after 6 clicks it misses 2, & then starts again,I will disconnect it and see what occurs. I'll find it.