Has anyone ever gotten dinged by police for turning left when a left turn arrow won't turn green since you're not heavy enough to trip the sensor? I'm just wondering what most people do. There are a lot of lights like that in my area. Or even regular green lights that require a weight sensor to go off... sometimes there are crosswalk buttons you can press but getting over to them isn't necessarily safer....

Actually, they are generally detector loops (like a metal detector), rather than weight sensors. There is simply a loop of wire embedded in the pavement. Frequently, smaller vehicles (bikes and motorcycles) don't actually register high enough to trip the sensor. You can try unclipping and laying your bike flat over the loop to trip it (unless it's carbon), but many states have laws allowing bikes and motorcycles to pass through after stopping and ensuring that the way is clear. Check your local ordinances.

Bking's right. Depending on where you are, it's legal for you to proceed after stopping for a light that won't change.

thanks for the clarification and advice

A friend got a warning ticket for this. The cop was even sympathetic, but wrote the ticket anyway.

Sensors are usually a rectangle with a middle line (lengthwise). Unless the road has recently been resurfaced, you can usually see the lines. For best chance, you want to be dead center in the box, directly over the center line. Leaning the bike over slightly is supposed to help.

You might try appealing to your city engineer. They can sometimes adjust the sensitivity to make it more likely to detect a bike. I live in a very bike-friendly city and almost all of the sensors will detect a bike. They even paint a picture of a bike directly over the optimum place to stop. On intersections with bike lanes, they even put a separate little sensor in the bike lane.

The other main type of sensor is a camera sensor. If you don't see any lines on the road, look across the intersection at the boom holding the light. See if it has a camera on it pointed at you. I have found these even more reliable than the loop in the road. These often turn the light green before I even need to stop.

I wish the street pavers/engineers in my area were more bike sensative. Recently a stop sign was turned into a stop light, the bike logo on the ground is next to (as opposed to on top of) the sensor. I can roll, stand, sit, jump..... on the sensor (not the logo) as much as I want but the light only changes when a car rolls up behind me. Many time I'd like to roll through the light but there's too much traffic in other directions to do that without certain bodily harm.