The THD quickly and effectively targets all ferrous, non-ferrous and stainless steel weapons, contraband and other metallic objects. It's unique 360 Degree, 3.5 inch detection area allows unrestricted scanning angles for fast and accurate hands-free body searches. No tools are required for replacing the 9V battery (included). Three LED function lights are included on the THD: green indicates the unit is on, amber indicates the THD's battery is low and red indicates metal detection.