The Spy Shop Team would suggest using a Bug Detection Device, like RF Frequency Checkers or a Professional Full Range GSM Signal Finder!
Detects frequencies on CDMA, GSM, DCS and PHS (3G) mobile phone signal in 1-10 meters.
Detect wide bands:
a. Can detect the RX frequency(CDMA) 824Mhz-849MHz
b. Can detect the RX frequency(GSM) 890MHz-915MHz
c. Can detect the RX frequency(DCS) 1710MHz-1785MHz
d. Can detect the RX frequency (PHS/3G) 1920MHz-1980MHz (2100-2200)
Earphone extra, for detecting in silent mode.
Antenna: Inner omni antenna
Power: 3.7V rechargeable lithium battery
Working Time: 2-3hours after fully charged
Environment temperature: -20c- +60c
Relative humidity: 30%-70%