For the past 6 months I have been using the cat eye orbit wheel light. It clips onto my bicycle wheel spokes. By squeezing the housing the light turns on. It makes a soft, but bright, illuminated glow which spins with my bike wheel while riding down the road. I have seen car drivers noticing the lights.
There are two remarkable things about the orbit. First, in 6 months of parking my bike on the street I have not had to change the battery once. Second, ask any cyclist in San Francisco how long they expect their bike to last before it’s stolen
by some thieving hipster. The answer is “not long.” I don’t have to worry about the orbits being stolen because they look like old fashioned reflectors.
I love ‘em.
There is a similar product from Nite Ize called the Spoke Lit, but I haven’t tried it.
[Note: Some people have complained about these being shipped in "try me" mode. To turn it off simply push and hold the button for 10 seconds or until the light flashes rapidly and then let go.-- OH Tips from the comments: Placing the Cat Eye on the seatpost back and headtube front rather than the spokes makes them visible from behind and head-on. This diffuses the beam over a wide area so it's visible from all directions. To prevent theft you can seal off the gap with epoxy and make them permanently attached, since the battery goes in on the non-spoke side. Also, flash mode makes the batteries last much longer.]
To see them in action along with CatEye's other product the Loop, check out this video: