The Loop Sensor Activator is a device for bicyclists that allows a low-weight velocipede to trigger traffic loop sensors. I had no idea there was a need for such a thing, but apparently, the problem's bad enough that a bicyclist can find themselves stranded at an intersection at a perpetual red short of flinging their bike violently to the ground:
A common problem for bicyclists, and in particular for bicycle commuters, is the traffic loop sensor. These are the devices which detect the presence of vehicles to control the sequencing of traffic lights at many intersections. Often, they are installed in figure-eight slits cut into the pavement near a traffic light.
The way they work is to detect the slight change in inductance of the loop of wire buried in the slit caused by a large metallic object (such as a motor vehicle) above the loop. The problem for bicyclists is that traffic departments often feel compelled to set the sensitivity of the electronics behind the loop rather low, so that false detections are avoided. This can make it difficult for a bicycle (a relatively small metal object) to make its presence known to the sequencing circuit. The result is a lot of frustration for a bicyclist trying to get a green light or left-turn arrow. This can be especially frustrating at streets with low traffic (often where these sensors are used in the first place), as one waits for a motor vehicle to come by and trip the sensor. Sometimes one must resort to laying the bicycle down on the road surface above the loop with the hope that the extra metal presented to the loop will cause detection. Sometimes it doesn't work, and sometimes frames aren't made of metal.
Various devices have been patented in order to address this problem. Some are a little impractical, and some don't work with modern loop sensor circuitry. One patented solution (see USP 5,652,577) has the bicyclist laying down a big piece of metallic foil or screen right on the road surface!.
Christ, what you American bicyclists have to put up with. Here in Zembla, every street has bike paths, bicyclists are respected and feared in equal measure and there are even traffic lights for bikes only. Do I amaze you?