Normally, by a near-field receiver. I don't know of any other way. An AM band unit is about $110 and an FM band unit is $200-400. I've seen ads for the AM band and I saw the FM unit at Hamvention in Dayton. The AM band unit can detect FM transmissions, you just can't hear the traffic, it's just quiet. It was also advertised to be able to detect leaking microwaves, etc. If I understand it, nearfield receivers and frequency counters rely on the relative strength surrounding a transmitter at close range to sync with the frequency. No tuning at all.
How would one go about detecting any suspected eavedropping devices in one's home in an inexpensive fashion? Sorry about the off-topic question, but what the heck.
sdw -- Stephen D. Williams Local Internet Gateway Co.; SDW Systems 513 496-5223APager LIG dev./sales Internet: sdw@lig.net CIS 76244.210@compuserve.com OO R&D Source Dist. By Horse: 2464 Rosina Dr., Miamisburg, OH 45342-6430 GNU Support ICBM: 39 34N 85 15W I love it when a plan comes together