I have had similar issues to Glen with this product and it is not limited to a single lemon unit, I have tried 3 different sensors. The sensors extremely prone to electrical interference. I purchased this item so that I could use it both outdoors and indoors on my trainer in the winter. First time I got it home I tested the unit to make sure it was responding, everything seemed to be working well so I mounted the bike on the trainer. I then turned on the TV, got on the bike, and bam, double 00 for speed and 0 cadence. I then tried making adjustments to see if I bumped something when I got on the bike but nothing would work. If I move the sensor very close to the transmitter everything seemd to work fine but that was when the computer was within ~20 cm of the transmitter and it is rated for 100cm. Finally I gave up, finished my workout and took the bike back to the store for service. They tested it and everything worked perfectly in store. So I took it home again, set it up, test it, everything is great. Later that evening I go for another workout, turn on the tv, get on the bike, again nothing. As you can guess I had a few choice words at that point. When I eventually calmed down I realized that it must be some interference coming from electronics in the area. Sure enough, turn the tv on, nothing works, turn it off, everything is perfect. As you can guess this product is going back. As with Glen, I also tried numerous times to contact Cateye but never received a single response. Save your money and give it to a company that actually cares about their customers. This is a terrible product from a company with no customer support.