Rather than edit my last post and correcting my understanding about the wireless bike computers, I'd like to add the following cut & paste information I received in an email from my contact at Sigma:
<span style="font-style: italic"><span style="font-weight: bold">"The wireless is low frequency R/F. The transmitter and receiver do not necessarily need to see each other. They have a maximum transmission distance of 70cm. However, people have tried to mount them to motorcycles in the past and found that electronics (starter switches, dimmer switches on headlights...) may interfere with the wireless transmission. For wireless our filings with the FCC as sports electronics require that we cannot interfere with anything but that anything can interfere with our products."</span></span>