These devices turn a normal daytime running light (or high beam) into a flashing light, about 4 times per second.  The light doesn't really flash but goes from about 50% to full bright, 4 times a second.  They are legal in all 50 states for daytime use only and have great benefit on motorcycles since many drivers don't associate light with a vehicle.  Commercial units have a daylight sensor to permit use only during daylight conditions.

Anyhow, I made one for my motorcycle.  I made mine function only on high beam as I want to draw attention only when necessary and not annoy other drivers when it isn't.  Well, let me state that it REALLY WORKS!  

I saw a driver trying to enter my lane of traffic from a driveway (actually a strip mall parking lot).  He was creeping and there were no other vehicles (cages) near me.  I was effectively invisible to him until I hit my high beam switch.  I glanced down to see my high beam indicator flashing, showing the high beam was also flashing.  He stopped in his tracks and gave me some kind of WTF face.  Hey, my bike is blue.  He probably is wondering what kind of cop I am

If you ride, I recommend getting one that you can select on command.  You will respect my authoraTAY!

Wing'ers around here mostly use them. Do they work? Probably. I just ride with highs on during the day (ironically a state trooper told me to do this). It does get SOME peoples attention, but not all. Since my bike has dual headlights I was thinking about adding something likt that to one headlight (right side probably) so only one flashes and have it set up so I can turn it on and off at will. But probably get a ticket for it here since the local PD has it ut for ALL bikes now (new chief is anti-motorcycle and proved it by having the cops ticket anyone on the MDA ride who blocked an intersection to keep the 2500 riders in a group for a charity ride).