Although once popular these two are no longer being made by professional metal detector manufacturers. BFO's may still be around but they are normally confined to cheap, toy type detectors. The word motion indicates that the search- coil requires movement in order for both ground control and discrimination to be achieved. Today's motion discriminators require very little movement of the searchcoil in order to identify a target. This advancement has taken much of the fatigue out of metal detecting.
Several innovations deserve special mention.
Surface mount technology has now opened the doors to miniaturization, permitting extremely compact designs. A select number of detectors are now available which utilize these hybrid circuit boards, though only available through select manufacturers at this time. This great achievement permits complex circuitry to be designed into small control housings. This greatly reduces the weight and bulkiness of the unit without sacrificing performance of the instrument. In fact, when properly engineered, this innovation provides even greater results, including virtually trouble-free operation.