This very bright, inexpensive tailight has become ubiquitous since its introduction a couple of years ago.  The large top bulb is a 1/2 watt LED.  In steady mode this bulbs stays on, in flashing mode the bright bulb alternated with two other LED’s below it in a very conspicuous flash pattern.  Hardware to attach the light to a seatpost or seatstay is included. I’ve been able to use the included hardware to mount the light to a rear rack as well.  The light is easily removable without tools from the bracket so you don’t have to leave it on the bike while parked in high theft areas.

Runs on AAA batteries (included).