Any of the Optoelectronics Frequency Counters and Nearfield Receivers may be used to detect wireless transmitters, or "bugs". The main function of all these units is to detect RF from nearby transmitters. All have different features than the next and some are more effective at detecting low power RF bugs than others.
30MHz-3GHz super sensitive Nearfield Receiver
30MHz-2GHz super sensitive Nearfield Receiver
10MHz-2.6GHz digital and analog Frequency Counter
50Hz-2.8GHz Frequency Counter
10MHz-1.4GHz Frequency Counter
50Hz-6GHz RF Detector