KJB Security SK199 Auto RF Pen Detector with UV Light. Detects wireless RF and UV devices.  Light will blink based on proximity to detected device. Approxmiately 4 weeks of battery life (depending on use). Detects wireless RF and UV devices Light will blink based on proximity to detected device Approxmiately 4 weeks of battery life (depending on use) Automatic RF detection Built-In anti mobile phone interference Frequency range 100MHz to 3GHz Currency checker Functioning Ink Pen Detects a radius of 1-10 meters Precisely detect wireless signals of 900/1200/1300 and 2400/2600/3000MHz