Phantom RT6L Mini Micro Red Dot Scope Sight w/ Smart Ambient Light Sensor AAA Battery All the best features from a super lightweight and compact sight Smart ambient light sensor on top automatically set the intensity of the dot Auto light control mode can be bypassed by a push on power switch and then manually control intensity of the dot by pushing and holding on intensity UP or DOWN switch Push button light switches keep last intensity setting when power is turned back on Use one AAA akaline battery