There is no such thing as a magnetic sensor for a traffic light.... it is either optical or induction loop -which is like a metal detector and can pick up *many* metals, not just steel. Induction loop sensors should be able to pick up a bicycle if they have been calibrated properly. If it does not sense you contact your local DOT to see if you can have it change. In fact one of the few lights in this area that I find I cannot change is an optical one that uses a camera. I'm just not big enough for it to see.

Oakleaf is correct that many jurisdictions will allow you to proceed through a red if you cannot change it. How long you have to wait and if this is allowable will depend on where you are, so look up your local traffic laws.