LIGHT SENSOR - This LED light will flash in nighttime and will not flash in daytime. (You can cover the other end by dark paper if you want it to flash in daytime.) NO BATTERY NEEDED - Solar energy can be absorbed and saved in high efficiency solar cells. It's powered by solar. It can blink for whole night after enough sun shining in daytime. NO WIRE NEEDED - Easy to install and looks clean on your dash panel, just stick it to the roof of the vehicle with corresponding glue.This LED alarm light does NOT require a car alarm system. PLEASE NOTE THAT - The light need to be put under sunshine directly. Sunshine above the dashboard is enough.It can be charged by solar whether you put switch to "on" or "off". Switch is tiny. You need a ballpen or little stick to push it.