Does anyone have any straightforward explanation for this behaviour so I dont start thinking up weird and wonderful causes.....

In the last 2 years of owning this car and through multiple new batteries for the key the only time it ever fails to unlock or lock is at about 9pm outside my house and the local supermarket a few hundred yards up the road. It just fails totally though the key led is lighting up so I have to unlock by the key and get the key in the ignition to silence the alarm. Then at the end of the trip (usually out to a call or the surgery) it locks fine. One time it unlocked fine at this time but in the carpark at the supermarket (yes I am lazy!) it wouldnt lock and a guy with a newish saab was having exactly the same problem and he said it only ever happens at that shop.

It surely cant be a battery in the car issue as it always works fine in the morning whether I am called out or not and has never once not worked at any other time of day.

Anyone any thoughts?

T

I know this will sound weird, but it could be the truth.

Do you have a telephone mast, radio station/antenna or someone with a ham radio nearby. It sounds exactly like something is interfering with the rf signal from the key transmitter.

I have a Kawasaki ZX6R motorbike with a Datatool alarm and it can get 'spiked' by strong radio signals. Once I couldn't switch off the alarm in a petrol station and had to push the bike out of the station before my alarm fob would switch the alarm off...much to the amusement of several motorists!!

I've also heard of this happening to other bike users and motorists.

Sounds like local RF interference to me if its happening in the one place and has been experienced by another motorist. Can't imagine what could be transmitting an RF signal from a shop strong enough to block yours but that's what it sounds like to me. 4.4 TDV8 Vogue Baltic Blue MY11

OK fair enough. No idea if there are any masts nearby and only at that time of night unless its a hobby sort of thing?

Strong electrical currents also interfere with keys, so a mat of wires in roof canopy under heavy load as lights are staring for instance will do this, as well as radio signals such as ham or CB radios. Already posted the story of 3 RR being towed out of horse trial carpark which wouldn't start due to over head power cables TDV8 Vogue SE 2009.
TDV8 Sport. Gone. Loved it but it didn't love me!
Other toys in the cupboard.......

I installed a remote operated halogen floodlight covering someones driveway many years ago - after demonstrating operation to her I handed the keyfob over and she tried it but it wouldn't work - she noticed she was stood on a manhole cover at the time and took 1 step to the right and tried again and it worked fine every time. I stepped onto the manhole cover and exactly the same deadspot.

Weird thing was it was a long range unit and we were only 10ft from the receiver and would happily work if I crossed the road and walked a few houses away but would never work if you stood on the manhole. She was convinced it was 'lay-lines' as she was a bit hippy-dippy.