The Spy Shop Team would suggest using a Bug Detection Device, like RF Frequency Checkers or a Professional Full Range GSM Signal Finder!
Signals Detected: 900/1200/1300/2600/3000MHz
Detection Indicator: Multicolor Flashing LED Lights
UV Light built into the back of the pen
Power Source: x3 LR-44 Batteries (not Included)
Dimensions: 146mm x 10mm x 10mm (L x W x D)