RF1 - Sniff-It RF Detector Probe Very sensitive RF detector probe connects to any digital multimeter and provides a DC voltage output from weak RF signals. This allows very easy tracing of low level RF signals that a counter can not pick up. Wide frequency coverage of 100 KHz to over 1000 MHz lets you track down most any problem in transmitter chains, receiver stages, or even complex PLLs. Works great as a sensitive field strength meter, too.