The Romeo Zero works off motion activation. It will turn on when it detects motion and shut itself off after a period of time when no movement is detected. There is a small button to adjust the brightness just behind the lens that will adjust the brightness level of the optic. There is no ON/OFF button.
The button right behind the display changes the brightness and also turns it on and off besides the the function of motion when it is on. Kevins answer is incomplete.
Previous answer is MOSTLY correct. If you hold down the brightness button for 2 seconds it will turn the unit off / on.
It turns off automatically after a period of undetected motion. It can also be turned off manually by pressing and holding the brightness button for two seconds. You turn it back on using he same action.
Yes you can turn it off. Hold the small button, that changes the brightness, for 2 seconds or longer. It will shut off, else you will run your battery down.