Cyclometer interference from car detection loops? I've noticed several times lately when stopping at an intersection with a car detection loop that my wireless cyclometer (an Atom 4.0) exhibits some strange behavior. It continues to think I'm moving (as indicated by a triangle icon), the distance increases (by a tenth of a mile every few seconds), the average speed goes up rapidly (in accordance with the distance increase), but the current speed appears stuck at whatever the last real reading was, and the maximum speed is unaffected.

I suspect it's to do with the car detection loops in the pavement, since the only other electronic things on my bike are lights, and I've seen this with them off. Is this how interference might present itself in the cyclometer? Are the loops indeed a probable source? Can I try to shield something to avoid it?
The car induction loop seems to be the most likely culprit. Their operation rely on an induction coil being buried under the street in front of the lights [1]. When it detects a car, or for that matter your metal bike, as a result its magnetic field is increased. This magnetic field is used for operation of the lights, but its conceivable that the field will affect the operation of your wireless comp. It's questionable if it would affect a wired computer, as it would be shielded with the connecting cable.

When passing through the door in my local bike shop with my bike while having my cyclocomputer fitted I also see the same affect. This time its down to the anti-theft magnetic detection loops fitted at the door. [2]

I suppose the solution is to fit a wired comp instead. Or else make sure you stay well back from/in front of the lights.

[1] http://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/question234.htm

[2] http://en.wikipedia.org/wiki/Electronic_article_surveillance#Magnetic_systems