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What caused the radio frequency of my Subaru Legacy's keyfob to go 'off beam'?

Last week, when 40 miles from home, my key fob failed to start my 2004 Subaru Legacy. I had to phone my wife to bring the spare key, which worked perfectly. I assumed it was the battery, but the Subaru agent (Prosport of Stockport) said that the frequency needed resetting. In half an hour he duly reset the key fob, checked the spare key, and all was well again.

I asked him why the frequency had gone 'off beam'. He thought it could be because of interference from some outside source: eg other car users or mobile phones or TV masts. Other customers came with the same problem, not often but from time to time. It was just my bad luck. Is this a frequent problem? Is the best precaution to carry a spare key? Or should we ask for the key fob to be revalidated at the annual inspection?

Asked on 3 April 2011 by JA, Stockport

Answered by Honest John
There is an EC Electronic Interference Directive, but car keyfob radio transmitters emit such a weak signal they can easily be swamped by stronger legal transmissions by radio hams or security systems. More here: www.ofcom.org.uk/static/archive/ra/topics/low-powe...m

Infra red makes more sense for cars.
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