Surecom SF401 Plus Frequency and Continuous Tone-Coded Squelch System (CTCSS) tester, shown next to a Motorola EX600XLS UHF radio. This tester was bought to be a small device that could be used to find the sub audible tones in use on radios in the field, when away from the bench test equipment. Sometimes you have to key the radio a few times to get the tones to show up properly, or adjust the distance between the radio under test and the Surecom tester. Using them a foot or so apart appears to work the best. This model will also show the frequency of your home WiFi system, and pressing the test button over and over lets you see it change.