usemethods of wiretap, bug Detection
http://www.bugsweeps.com/info/wiretap_detection.html
http://www.spytechs.com/bug_sweep_equip/default.htm
also common metal and ore detection methods -coin, ring, jewelry detectors
perhaps cut off activation signal in detector since customer device is active.
choice is active search or passive search
many interesting stories of spy equipment
casinos can scan for electronic devices on customers with stored signatures for recognition